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Lloyd Stagg
Lloyd Stagg
최근 활동: 2025년 5월 6일

I like this problem by James and have solved it in several ways. A solution by Natalie impressed me and introduced me to a new function conv2. However, it occured to me that the numerous test for the problem only cover cases of square matrices. My original solutions, and Natalie's, did niot work on rectangular matrices. I have now produced a solution which works on rectangular matrices. Thanks for this thought provoking problem James.
I just now discovered Discussions.
Can anyone provide insight into the intended difference between Discussions and Answers and what should be posted where?
Just scrolling through Discussions, I saw postst that seem more suitable Answers?
What exactly does Discussions bring to the table that wasn't already brought by Answers?
Maybe this question is more suitable for a Discussion ....
Alexander
Alexander
최근 활동: 2024년 1월 10일

Ich habe das Problem das ich immer nur 1 Tag aufzeichnen kann (siehe Anhang), obwohl ich den Parameter au 15 tage gestellt habe.
im trying to draw a path for the aircraft. so the aircraft needs to avoid all the red zones in the radar image i have and should travel only on green zones even the waypoints are on redzones.
% Load the radar image
radar_image = imread('radar.jpg');
I = radar_image;
% Display the radar image
figure;
imshow(I);
% Select waypoints
disp('Select the waypoints:');
[x, y] = ginput;
waypoints = [x, y];
% Save waypoints
save('waypoints.mat', 'waypoints');
% Load saved waypoints
load('waypoints.mat');
% Plot waypoints and connect them with lines
hold on;
plot(waypoints(:, 1), waypoints(:, 2), 'ro', 'LineWidth', 2);
plot(waypoints(:, 1), waypoints(:, 2), 'r--', 'LineWidth', 1);
% Load aircraft icon image
aircraft_icon = imread('aircraft_icon.png');
% Resize the aircraft icon image
desired_size = 30; % Change this value to adjust the size of the aircraft icon
aircraft_icon_resized = imresize(aircraft_icon, [desired_size, desired_size]);
% Animate aircraft using AI algorithm
tolerance = 5; % Tolerance for reaching waypoints
max_steps = 100; % Maximum steps to reach the destination
step_size = 1; % Step size for potential field calculations
% Plot the initial position of the aircraft
current_pos = waypoints(1, :);
h = image(current_pos(1), current_pos(2), aircraft_icon_resized);
set(h, 'AlphaData', 0.7); % Set the transparency (optional)
for i = 1:size(waypoints, 1)-1
start = waypoints(i, :);
finish = waypoints(i+1, :);
% Perform A* algorithm to find an alternate path through green zones
alternate_path = A_star(start, finish);
for j = 1:size(alternate_path, 1)-1
% Initialize the position of the aircraft
current_pos = alternate_path(j, :);
next_waypoint = alternate_path(j+1, :);
% Continue to the next waypoint if the current position is already near the waypoint
if norm(current_pos - next_waypoint) <= tolerance
continue;
end
% Perform animation to move the aircraft through the potential field
animateAircraft(current_pos, next_waypoint, max_steps, step_size, h);
% Update the radar image I with the current position of the aircraft
I(round(current_pos(2)), round(current_pos(1))) = 0;
end
end
function animateAircraft(current_pos, next_waypoint, max_steps, step_size, h)
% Animate the aircraft to move from current_pos to next_waypoint
for t = 1:max_steps
% Check if the aircraft has reached the destination waypoint
if norm(current_pos - next_waypoint) <= tolerance
break;
end
% Calculate potential field forces
attractive_force = next_waypoint - current_pos;
repulsive_force = zeros(1, 2);
% Calculate the repulsive forces from each red and yellow region
red_regions = find(I == 1);
yellow_regions = find(I == 2);
for k = 1:length(red_regions)
[r, c] = ind2sub(size(I), red_regions(k));
obstacle = [c, r];
repulsive_force = repulsive_force + calculate_repulsive_force(current_pos, obstacle);
end
for k = 1:length(yellow_regions)
[r, c] = ind2sub(size(I), yellow_regions(k));
obstacle = [c, r];
repulsive_force = repulsive_force + calculate_repulsive_force(current_pos, obstacle);
end
% Combine the forces to get the total force
total_force = attractive_force + 0.5 * repulsive_force; % Reduce repulsive force to move through obstacles more easily
% Normalize the total force and move the aircraft
total_force = total_force / norm(total_force);
current_pos = current_pos + step_size * total_force;
% Update the aircraft position on the plot
set(h, 'XData', current_pos(1), 'YData', current_pos(2));
drawnow; % Force the plot to update
% Pause for a short duration to visualize the animation
pause(0.05);
end
end
function force = calculate_repulsive_force(position, obstacle, I)
% Constants for the potential field calculation
repulsive_gain = 1000; % Adjust this value to control the obstacle avoidance strength
min_distance = 5; % Minimum distance to avoid division by zero
% Calculate the distance and direction to the obstacle
distance = norm(position - obstacle);
direction = (position - obstacle) / distance;
% Check if the obstacle is a waypoint
is_waypoint = false;
waypoints = [1, 2; 3, 4; 5, 6]; % Replace this with the actual waypoints' coordinates
for i = 1:size(waypoints, 1)
if isequal(obstacle, waypoints(i, :))
is_waypoint = true;
break;
end
end
% Check the color of the obstacle in the radar image
color = I(round(obstacle(2)), round(obstacle(1)));
% Calculate the repulsive force
if ~is_waypoint && color ~= 0 % Obstacle is not a waypoint or 0
force = repulsive_gain / max(distance, min_distance)^2 * direction;
else
force = zeros(1, 2);
end
end
this the code im using. But according to the output im getting, the aircraft is still travelling through all the red and yellow zones.i have tagged the aircraft_icon.png and rada.jpg images which have been used in the code. can somebody help me out with this?
I recently have found that I am no longer able to give my difficulty rating for questions on Cody after sucessfully completing a question. This is obviously not a big deal, I was just wondering if this was an issue on my end or if there was some change that I was not aware of.
The option to rate does not pop up after solving a problem, and the rating in general does not even show up anymore when answering questions (though it is visible from problem groups).
When solving problems over on Cody, I can almost always view all solutions to a problem after submitting a correct solution of my own. Very rarely, however, this is not the case, and I instead get the following message:
This solution is locked. To view this solution, you need to provide a solution of the same size or smaller.
You may solve another problem from Community group to unlock all the solutions to this problem.
If this happens, then again, I can almost always rectify this by submitting a (correct) solution to a different problem (I take it that the Community group is the implicit group of all problems on Cody --- is it?). But sometimes that, too, fails.
So my question is, why? What are the criteria that determine when all solutions are, in fact, unlocked?
(There is a related question here, but I feel the posted answer does not answer the question.)
Tom BS
Tom BS
최근 활동: 2022년 11월 15일

Hello,
Can someone please give me a hint how the settings at Tasmoto have to be made in order to send data via MQTT to ThingSpeak.
Halil Kemal has an open channel tag: tasmota where this seems to work.
Thank you in advance for your support.
TOM
We operate roughly 600 data loggers on Think Speak where there are roughly 150 gateways and each gateway communicates with a node. Our channels are labeled node# - gateway number and each number is 16 diigits. We have not found a wildcard search function so must have each number exactly right or we cannot find our channel. In some cases we wish to query a gateway and see which nodes are successfully communicating with it.

I have a Thingtweet: "Measurements %%datetime%% Comment" The tweet will send the time as say: 5:23pm I want it in 24hr format = 17:23 I have scoured the site and I cant find any way of doing this in a tweet. Also that would be local time, is it possible to use UTC ?

Bonjour, J'utilise arduino Mega 2560 avec le shield Ethernet. Le sketch ino joint ci-après me permet de visualiser la jauge dans la page index.htm chargée sur la carte SD. ThingSpeak affiche bien le graph correspondant. Mais ma page web n'y a pas accès. Comment intégrer les codes dans la page ou dans le sketch pour cela ? Je vous joins la capture d'écran de cette page ainsi que les codes De la page et du sketch. Merci pour votre aide.

*********************************** Code Page "index.htm" ***********************************

<!DOCTYPE html>
<html>
    <head>
        <title>Arduino Internet Voltmeter</title>
        <script>
		var data_val = 0;		// raw data from Arduino analog input (0 to 1023)
		var volts = 0;			// voltage calculated from Arduino analog raw data value
		var num_updates = 0;	// number of 200ms periods used to calculate time to send data to ThingSpeak
		// gauge code
		eval(function(p,a,c,k,e,r){e=function(c){return(c<a?'':e(parseInt(c/a)))+((c=c%a)>35?String.fromCharCode(c+29):c.toString(36))};if(!''.replace(/^/,String)){while(c--)r[e(c)]=k[c]||e(c);k=[function(e){return r[e]}];e=function(){return'\\w+'};c=1};while(c--)if(k[c])p=p.replace(new RegExp('\\b'+e(c)+'\\b','g'),k[c]);return p}('t W=v(f){W.2t.3T(A);A.B={Z:2u,19:1q,1h:1q,1J:U,1b:D,K:0,V:[\'0\',\'20\',\'40\',\'2A\',\'2B\',\'D\'],2r:10,2C:M,1E:U,2q:{2D:3,2E:2},2H:M,1c:{2j:10,2m:3y,2O:\'3v\'},J:{2P:\'#4h\',V:\'#31\',2r:\'#3k\',1J:\'#37\',1E:\'#37\',3e:\'#31\',1t:{2s:\'1e(3Y, 3d, 3d, 1)\',3c:\'1e(1Y, 5I, 5E, .9)\'}},1o:[{1n:20,1D:2A,1F:\'#3j\'},{1n:2A,1D:2B,1F:\'#36\'},{1n:2B,1D:D,1F:\'#5n\'}]};t g=0,1p=A,N=0,1S=0,1G=U;A.5d=v(a){N=f.1c?g:a;t b=(f.1b-f.K)/D;1S=a>f.1b?1S=f.1b+b:a<f.K?f.K-b:a;g=a;f.1c?3l():A.1g();C A};A.3m=v(a){N=g=a;A.1g();C A};A.4T=v(){g=N=1S=A.B.K;A.1g();C A};A.4R=v(){C g};A.13=v(){};v 2k(a,b){Q(t i 4P b){z(1H b[i]=="1W"&&!(4O.4y.2V.4p(b[i])===\'[1W 4n]\')&&i!=\'Z\'){z(1H 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m=3J(2w[j]).1j(/\\s+/),1Q={};z(m[0]&&m[0]!=\'\'){1Q.1n=m[0]}z(m[1]&&m[1]!=\'\'){1Q.1D=m[1]}z(m[2]&&m[2]!=\'\'){1Q.1F=m[2]}B.1o.3T(1Q)}26}2y\'1c\':{z(f[1]){z(!B.1c){B.1c={}}z(f[1]==\'2O\'&&/^\\s*v\\s*\\(/.5H(I)){I=3U(\'(\'+I+\')\')}B.1c[f[1]]=I}26}5J:{t n=2F(f);z(n==\'13\'){2z}z(n==\'V\'){I=I.1j(/\\s+/)}O z(n==\'2C\'||n==\'2H\'){I=I==\'M\'?M:U}O z(n==\'2q\'){t o=I.1j(\'.\');z(o.H==2){I={2D:2c(o[0]),2E:2c(o[1])}}O{2z}}B[n]=I;26}}}}t g=2v W(B);z(d.18(\'1k-3V\')){g.3m(1R(d.18(\'1k-3V\')))}z(d.18(\'1k-13\')){g.13=v(){3U(A.B.Z.18(\'1k-13\'))}}g.1g()}}});',62,358,'||||||||||||||||||||||||||ctx|||var|max|function||||if|this|config|return|100|Math|lineTo|save|length|attrValue|colors|minValue|fillStyle|true|fromValue|else|beginPath|for|restore|radians|fill|false|majorTicks|Gauge|||renderTo||||onready|CX||arc|CY|getAttribute|width|PI|maxValue|animation|cctx|rgba|r2|draw|height|cache|split|data|lgrad|prop|from|highlights|self|200|rOut|ss|needle|rIn|style|rpoint|font|CW|rotate|CH|pad2|closePath|to|units|color|imready|typeof|text|title|moveTo|pow|progress|ea|sin|sa|hlCfg|parseFloat|toValue|cos|270|addColorStop|object|stroke|255|substr||025||quadraticCurveTo|||break|fillText|initialized|cfg|r1|clearInterval|parseInt||lineWidth|center|delta|textAlign|px|delay|applyRecursive|pad1|duration|shadowColor|shadowBlur|appendChild|valueFormat|minorTicks|start|Collection|null|new|hls|setInterval|case|continue|60|80|strokeTicks|int|dec|toCamelCase|window|glow|styleSheet|i8d|drawValueBox|drawNeedle|baseInit|type|fn|plate|url|document|ie|81|strokeStyle|toString|th|90|Arial|tw|Led|444|padValue||cint|abs|ccc|888|shad|vd|pe|pe1|end|128|numbers|shadowOffsetX|shadowOffsetY|143|roundRect|eee|666|animate|setRawValue|05|045|012|004|getElementsByTagName|f0f0f0|r3|getContext|cycle|createElement|d0|250|drawUnits|cssText|styleSheets|body|drawTitle|domReady|drawNumbers|addEventListener|drawMajorTicks|drawMinorTicks|trim|drawHighlights|drawPlate|clearRect|attributes|round|translate|step|Date|_animate|push|eval|value|the|77|240|creating||when|ddd|aaa|specified||not|e8e8e8|f5f5f5|fafafa|drawImage|was|quint|element|quad|measureText|Canvas|fff|04|Error|07|createRadialGradient|throw|Array|babab2|call|linear|head|cloneNode|navigator|userAgent|toLocaleLowerCase|indexOf|msie|prototype|http|smart|ip|net|styles|fonts|digital|mono|eot|ttf|180|face|family|src|315|Object|in|css|getValue|elastic|clear|try|createTextNode|catch|sheet|createLinearGradient|updateConfig|div|fontFamily|position|absolute|overflow||hidden|innerHTML|setTimeout|parentNode|removeChild|get|string|setValue|id|number|93|DOMContentLoaded|attachEvent|onload|bounce|lineCap|toUpperCase|999|replace|canvas|91|canv|gauge|toFixed|d1|getElementById|item|nodeName|toLowerCase|88|d2|switch|acos|shift|122|85|delete|test|160|default|tagName|188'.split('|'),0,{}))
		// function called periodically to get analog value from Arduino using Ajax
		function GetArduinoInputs()
		{
			nocache = "&nocache=" + Math.random() * 1000000;
			var request = new XMLHttpRequest();
			request.onreadystatechange = function()
			{
				if (this.readyState == 4) {
					if (this.status == 200) {
						if (this.responseXML != null) {
							document.getElementById("input3").innerHTML =
								this.responseXML.getElementsByTagName('analog')[0].childNodes[0].nodeValue;
								data_val = this.responseXML.getElementsByTagName('analog')[0].childNodes[0].nodeValue;
								// calculate voltage
								volts = data_val * 3.5 / 1023;
								// only send data to ThingSpeak every 20 seconds or 100 x 200ms
								if (num_updates >= 100) {
									num_updates = 0;
									// send voltage to ThingSpeak
								ThingSpeakSend("xxxxxxxxxxxxxxxx", volts);	// insert your ThingSpeak Write API Key here
								
								}
								num_updates++;
						}
					}
				}
			}
			request.open("GET", "ajax_inputs" + nocache, true);
			request.send(null);
			setTimeout('GetArduinoInputs()', 200);	// send the request for Arduino analog data every 200ms
			
		}
		// function to send data to ThingSpeak
		function ThingSpeakSend(api_write_key, voltage)
		{
			var ts_req = new XMLHttpRequest();
			// GET request string - modify if more fields are needed
			var req_str = "http://api.thingspeak.com/update?key=" + api_write_key + "&field1=" + voltage;
			ts_req.onreadystatechange = function()
			{
				// not doing anything with response from ThingSpeak
			}
			// send the data to ThingSpeak
			ts_req.open("GET", req_str, true);
			ts_req.send(null);
		}
	</script>
    </head>
    <body onload="GetArduinoInputs()">
        <h1>Arduino Internet Voltmeter</h1>
        <p>Analog (A2): <span id="input3">...</span></p>
        <canvas id="an_gauge_1" data-major-ticks="0 0.5 1 1.5 2 2.5 3 3.5" data-type="canv-gauge" data-min-value="0" data-max-value="3.5" data-onready="setInterval( function() { Gauge.Collection.get('an_gauge_1').setValue(volts);}, 200);"></canvas>
        <!-- insert ThingSpeak chart code here -->
          <iframe width="450" height="260" style="border: 1px solid #cccccc;" src="https://thingspeak.com/channels/1620920/charts/1?bgcolor=%23ffffff&color=%23d62020&dynamic=true&results=60&type=line&update=20&yaxismax=4&yaxismin=0"></iframe>
  <!-- REPLACE THIS COMMENT WITH YOUR THINGSPEAK GRAPH -->
      </body>
  </html>

********************************************* Code "eth_websrv_SD_Ajax_gauge.ino" : *********************************************

#include <Ethernet.h>
#include <SD.h>
#include <ThingSpeak.h>
// size of buffer used to capture HTTP requests
#define REQ_BUF_SZ   50
// MAC address from Ethernet shield sticker under board
byte mac[] = { 0x90, 0xA2, 0xDA, 0x00, 0x1A, 0x71 };
IPAddress ip(192, 168, 1, 17); // IP address, may need to change depending on network
EthernetServer server(80);  // create a server at port 80
File webFile;               // the web page file on the SD card
char HTTP_req[REQ_BUF_SZ] = {0}; // buffered HTTP request stored as null terminated string
char req_index = 0;              // index into HTTP_req buffer
void setup()
{
  // disable Ethernet chip
  pinMode(10, OUTPUT);
  digitalWrite(10, HIGH);
    Serial.begin(9600);       // for debugging
    // initialize SD card
    Serial.println("Initializing SD card...");
    if (!SD.begin(4)) {
        Serial.println("ERROR - SD card initialization failed!");
        return;    // init failed
    }
    Serial.println("SUCCESS - SD card initialized.");
    // check for index.htm file
    if (!SD.exists("index.htm")) {
        Serial.println("ERROR - Can't find index.htm file!");
        return;  // can't find index file
    }
    Serial.println("SUCCESS - Found index.htm file.");
    Ethernet.begin(mac, ip);  // initialize Ethernet device
    server.begin();           // start to listen for clients
    Serial.print ("*\n -> Le serveur est sur l'adresse : ");
    Serial.println(Ethernet.localIP());
}
void loop()
{
    EthernetClient client = server.available();  // try to get client
    if (client)   // got client?
        {
          boolean currentLineIsBlank = true;
        while (client.connected()) 
        {
            if (client.available())    // client data available to read
                {
                char c = client.read(); // read 1 byte (character) from client
                // buffer first part of HTTP request in HTTP_req array (string)
                // leave last element in array as 0 to null terminate string (REQ_BUF_SZ - 1)
                if (req_index < (REQ_BUF_SZ - 1)) {
                    HTTP_req[req_index] = c;          // save HTTP request character
                    req_index++;
                }
                // last line of client request is blank and ends with \n
                // respond to client only after last line received
                if (c == '\n' && currentLineIsBlank) {
                    // send a standard http response header
                    client.println("HTTP/1.1 200 OK");
                    // remainder of header follows below, depending on if
                    // web page or XML page is requested
                    // Ajax request - send XML file
                    if (StrContains(HTTP_req, "ajax_inputs")) {
                        // send rest of HTTP header
                        client.println("Content-Type: text/xml");
                        client.println("Connection: keep-alive");
                        client.println();
                    // send XML file containing input states
                    XML_response(client);
                    }
                    else {  // web page request
                        // send rest of HTTP header
                        client.println("Content-Type: text/html");
                        client.println("Connection: keep-alive");
                        client.println();
                        // send web page
                        webFile = SD.open("index.htm");        // open web page file
                        if (webFile) {
                            while(webFile.available()) {
                                client.write(webFile.read()); // send web page to client
                            }
                            webFile.close();
                        }
                    }
                    // display received HTTP request on serial port
                    Serial.print(HTTP_req);
                    // reset buffer index and all buffer elements to 0
                    req_index = 0;
                    StrClear(HTTP_req, REQ_BUF_SZ);
                    break;
                }
                // every line of text received from the client ends with \r\n
                if (c == '\n') {
                    // last character on line of received text
                    // starting new line with next character read
                    currentLineIsBlank = true;
                } 
                else if (c != '\r') {
                    // a text character was received from client
                    currentLineIsBlank = false;
                }
            } // end if (client.available())
        } // end while (client.connected())
        delay(1);      // give the web browser time to receive the data
        client.stop(); // close the connection
    } // end if (client)
}
// send the XML file containing analog value
void XML_response(EthernetClient cl)
{
    int analog_val;
      cl.print("<?xml version = \"1.0\" ?>");
      cl.print("<inputs>");
      // read analog pin A2
      analog_val = analogRead(2);
      cl.print("<analog>");
      cl.print(analog_val);
      cl.print("</analog>");
      cl.print("</inputs>");
  }
// sets every element of str to 0 (clears array)
void StrClear(char *str, char length)
{
    for (int i = 0; i < length; i++) {
        str[i] = 0;
    }
}
// searches for the string sfind in the string str
// returns 1 if string found
// returns 0 if string not found
char StrContains(char *str, char *sfind)
{
    char found = 0;
    char index = 0;
    char len;
    len = strlen(str);
    if (strlen(sfind) > len) {
        return 0;
    }
    while (index < len) {
        if (str[index] == sfind[found]) {
            found++;
            if (strlen(sfind) == found) {
                return 1;
            }
        }
        else {
            found = 0;
        }
        index++;
    }
      return 0;
  }

Hi, i wonder if any one experiencing the same, but in my thing sepak profiel i can only see : 1- User API Key 2- Alert API Key

but no MQTT API key? not sure why Thank you

Hallo,

bei THINKSPEAK werden auf dem Handy max 60 Werte angezeigt.

Bei 1 Wert pro Stunde sieht man also 2,5 Tage.

Ich würde lieber 1 Wert pro Tag senden und damit 60 Tage im Überblick haben.

Gibt es dafür eine Lösung ?

Danke & MfG 

Peter Benger 

Dear Sir, I have configure the thing-speak account for our monitoring system.But I have two issue regarding this as shown below; 1.whatever the field i have configure in the channel number 1,2...8,with respective tag, same tag is not reflected on graph.i just shown to you for your reference in the attachments. 2 whatever the excel file is generating based on input data it takes 7 minutes of delay.after live capturing. can you please resolve this issue for me

Right now ThingSpeak supports up to 8 fields of data plus the status and three position fields. If you could have more fields, how many would you want? I have one channel of control settings for a project that I would have used up to 12, but no more than that.

Rik
Rik
최근 활동: 2025년 7월 7일

Similar to what has happened with the wishlist threads (#1 #2 #3 #4 #5), the "what frustrates you about MATLAB" thread has become very large. This makes navigation difficult and increases page load times.
So here is the follow-up page.
What should you post where?
Wishlist threads (#1 #2 #3 #4 #5): bugs and feature requests for Matlab Answers
Frustation threads (#1 #2): frustations about usage and capabilities of Matlab itself
Missing feature threads (#1 #2): features that you whish Matlab would have had
Next Gen threads (#1): features that would break compatibility with previous versions, but would be nice to have
@anyone posting a new thread when the last one gets too large (about 50 answers seems a reasonable limit per thread), please update this list in all last threads. (if you don't have editing privileges, just post a comment asking someone to do the edit)

Hello everyone,

I’m Jiro, and I’m part of the Education Customer Success group at MathWorks. We help academics, students, and institutions achieve success through the use of our tools. I will be the moderator for this new community of distance learning.

As many academic institutions are moving their classes online, we hope that this community will help instructors connect with others who are in the same situation. This community site gathers various resources and information that will be useful for teaching with MATLAB and Simulink in a distance learning setting. We have a number of MathWorks employees monitoring this community, but we want this to be a place for the community to come together. The hope is that the community will grow and the resources gathered here will grow with it.

I encourage you to share best practices ( Discussions ), ask questions ( MATLAB Answers ), and share examples ( File Exchange ).

As a first question, what course are you teaching (or planning to teach) online?

Jan
Jan
최근 활동: 2024년 10월 4일

After reading Rik's comment I looked for a list of Matlab releases and their corresponding features. Wiki: Matlab contains an exhaustive list, but what about having a lean version directly in the forum?
If this is useful, feel free to expand the list and to insert additions. Thank you.
Jan
Jan
최근 활동: 2013년 8월 9일

Some of Matlab's toolbox functions are affected by magic strings or magic numbers, which are strings or numbers with a deeper meaning besides the normal value. Both are considered as bad programming patters, because they provoke confusions, when the magic keys appear with the normal meaning by accident. See http://en.wikipedia.org/wiki/Anti-pattern
Example 1:
clear('myVariable')
clear('variables')
While the 1st clears the variable myVariable, the later clears all variables. Here 'variables' has a meta-meaning. The problem appears, when 'variables' is an existing variable:
a = 1;
variables = 2;
clear('variables')
disp(a) % >> 1
Only variables is cleared, which cannot be understood directly when its definition is 1000 lines before.
Example 2:
uicontrol('String', 'default')
This creates a button with the empty string '' instead of the expected 'default', because this is the magic string to invoke the default value get(0, 'DefaultUIControlString'). The same concerns properties of other graphic objects also, e.g. the 'name' property of figure or the string of uimenu. There is a workaround which allows the user to display 'default': Simply use '\default'. Unfortunately this is doubled magic, because in consequence it is impossible to display the string '\default'. Obviously a bad idea.
Example 3:
Graphic handles are doubles (although gobject of the new R2013a seems, like this is subject to changes? [EDITED: Yes, it changed with HG2 in R2014a]). But then a handle can be confused with data:
a = axes; % e.g. 0.0048828125
plot(a, 2, '+')
But you cannot draw the point [0.0048828125, 2] by this way, because the 1st input is considered as handle of the parent. Here all possible values of handles are magic. Collisions are very unlikely, but there is no way to avoid them reliably - as long as handles have the type double.
Question:
Which functions are concerned by magic values? What are the pitfalls and workarounds?
Don't be shy, what was your matlab learning curve, how many years or months, what were the difficulties to begin with.
I think that the answers would be most valuable for new users, maybe you can also tell us the tricks that allowed you to master some parts or all matlab.
Now it's your turn...
I love MATLAB. It is so quick and easy to write software to do what you want. It has excellent debugging and profiling tools. It is cross platform, making code easy to share (assuming the other people have forked out for the not-so-cheap license). It has interfaces to other software.
However, there are some things about it that irk me. I'd like to hear from other people what things annoy them about MATLAB.
---------------------------------
Because this thread has become so large it is slow to load and navigate. Please post new answers in the second thread.
---------------------------------