Some basic MATLAB questions

Okay, so I'm just starting to use MATLAB for engineering assignments. The assignment from my instructor requires us to write a loop using if, else if and else commands. Thats not what I have trouble with, but I need some assistance to come up with a way to take a number and assign it a letter grade based on the number. So the grading scale is like this:

0-59 - F 60-69 - D 70-79 - C 80-89 - B 90-100 - A

So I know I will start the first condition with if, but could someone do an example to show me how it is supposed to be set up? Please DO NOT do the whole thing, as I want to learn it on my own, but sometimes we need a bit of assistance.

Thank you

EDIT: Thanks to Matt for the first Question.

[Naftali]

% n - input numbers in array
% g - output grades
grades = 'FDCBA' ; 
k = min(max(floor(0.1*(n-50)+1,1),5) ;
g = grades(k) ;

Answer 1

[Matt Fig]

X = round(rand*6)

if X<3
  disp('Small X')
elseif X==3
  disp('X is 3')
elseif X>=3 & X<5
  disp('Medium X')
else
  disp('X is 5 or 6')
end

[nejib]

hello :

i need to have the the same amplitude!!!!

any help : !!

t = 0:1/1e3:10;
d = [0:2:60;sin(1*pi*0.1*(0:2:60))]';
x = @rectpuls;
y = pulstran(t,d,x);

plot(t,y)
hold off
xlabel('Time (s)')
ylabel('Waveform')

[Walter Roberson]

@nejib

Same amplitude:

t = 0:1/1e3:10;
d = 0:2:60;
x = @rectpuls;
y = pulstran(t,d,x);

plot(t,y)
hold off
xlabel('Time (s)')
ylabel('Waveform')

Answer 2

[Matt Tearle]

Thank you for your asking such a great question! Matt has basically given you all the info you need for this assignment, but, in the spirit of Sean's "not what you were asked, but some cool stuff you should know about MATLAB"...

x = randi(100,20,1)  % Make some grades
y = char(70*ones(size(x)));  % Everyone gets an F!
y(x>59) = 'D'        % Upgrade the Ds (and better)
y(x>69) = 'C'        % Upgrade the Cs
y(x>79) = 'B'        % The Bs
y(x>89) = 'A'        % And finally the As

Or (requires Stats TB, which you should have as a student)

y = ordinal(x,{'F','D','C','B','A'},[],[0,60:10:100])
hist(y)          % See the grades
pie(hist(y))     % Grade distribution
mean(x(y>='C'))  % The average score of those who got a C or better

[Sean de Wolski]

+1: ordinal can behave like histc(). Learn something every day

Answer 3

[Matt Fig]

As per requested:

% x is the numerical unknown grade
G = char(interp1([-inf,59,60,69,70,79,80,89,90,inf],['FFDDCCBBAA'],x,'n'))

or, for 2012+ versions:

G = char(interp1([-realmax,59,60,69,70,79,80,89,90,realmax],double(['FFDDCCBBAA']),x,'n'))

Answer 4

[Matt Fig]

Another one-liner (short!):

% x is the unknown numerical grade.
G = char(65+sum(x<.5+[59 59:10:89]));

As it stands it only works for scalar x. BSXFUN would cure that if it was needed, like so.

G = char(65+sum(bsxfun(@lt,x,.5+[59 59:10:89].')));

Answer 5

[Sean de Wolski]

I know this is not the purpose of your assignment, but here is a cool way to do it. The logic should be easily transmittable to if/else/etc instead of histc()

letters = 'FDCBA';
grade = 87
[~,idx] = histc(grade,[0 59:10:89 100+eps(100)]);
letters(idx)

[Matt Fig]

I like this one too!

char(interp1([-inf,59,60,69,70,79,80,89,90,inf],['FFDDCCBBAA'],87,'n'))

[Sean de Wolski]

I like it! Interestingly though, this no longer works in 12a.

Hump-day challenger tomorrow?

[Jan]

What is the error message in R2012a? But this does still work, I hope:

char(interp1([-inf,59,60,69,70,79,80,89,90,inf], double('FFDDCCBBAA'), 87, 'n'))

Please, Matt Fig, post your one-lines as an answer.

[Sean de Wolski]

Inf and Nan are non supported. Converting them to reasonable values, strings are not supported.

[Matt Fig]

Now why would support for inf be dropped? TMW does some strange stuff from time to time. (strmatch, findstr, etc...)

Answer 6

[Jan]

index = max(1, ceil(-4.9:0.1:5.1));
pool  = 'FDCBAA';
Grade = pool(index(x + 1));

Answer 7

[Yash Meshram]

i = input('Marks of the student: ');
if 0<=i && i<=59
    fprintf('F grade\n');
end

if 60<=i && i<=69
    fprintf('D grade\n');
end

if 70<=i && i<=79
    fprintf('C grade\n');
end

if 80<=i && i<=89
    fprintf('B grade\n');
end

if 90<=i && i<=100
    fprintf('A grade\n');
end

Answer 8

[hassan saher]

Use help command to get help about rand function.

Answer 9

[Vivek Sharma]

Please help me with the MATLAB code for the following problem. PDF is attached herewith.

Thank you.

[mahmood]

clc;
clear;

% Constants
c = 13.03;
p = 19.93;

% Initial temperatures
T1 = 576;
T2 = 439;

% Number of impacts
m = 5;

% Initialize variables
T = (T1 + T2) / 2;
E = zeros(m, 1);

% Perform m impacts
for i = 1:m
    E(i) = (c * p * T) / 23.5;
    T = (T1 + T) / 2;
end

% Display the values of E for each impact
disp('Values of E for each impact:');
disp(E);