Help with if statement in a calculation loop

Hello,

I have a problem with a code. I want to calculate some numbers but I want to "limit" my results via a loop.

I want values <1 to be =1, values with >10 to be 10 and the others to be calculated from this equation:

x= x*1.3+0.5. I wrote this code but it is not use

x= 5 + randn * 0.5
if x < 1
    x == 1
elseif x > 10
    x == 10
else x > 3
    x == 1.3* x -0.75
end

Where is the problem?

Thanking you in advance

[Nino Wyssen]

I can see several problems here.

First, Matlab likes the lines to be finished with a semicolon, but this isn't necessary if you don't mind your programm outputting all the operations.

Then, you aren't assigning values. You are comparing them. To assign a new value to a variable you only need one equal sign.

Third, you can't use a condition for you else statment, if you only wnt to execute the command below u need to use another elseif.

From your description I suspect the following code does the right thing for you:

x= 5 + randn * 0.5;
if x < 1
    x = 1;
elseif x > 10
    x = 10;
else
    x = 1.3* x -0.75;
end

even though I think it would be better to use a new variable for your result

x= 5 + randn * 0.5;
if x < 1
    y = 1;
elseif x > 10
    y = 10;
else
    y = 1.3* x -0.75;
end

[Ivan Mich]

I am sorry but running this code stil values up to 10 exist.

It is no use

Answer 1

[Stephen23]

The simplest and most efficient solution is to use MIN and MAX:

x = 5 + randn(5,7)*1.5;
x = x*1.3 + 0.5 

x = 5×7

7.6491 8.4519 8.8820 8.7385 9.8065 8.6945 8.5660 5.7131 13.1416 6.3650 9.1859 6.9860 9.4199 5.4750 8.8947 7.3018 6.4618 7.2714 9.2859 8.7553 5.7112 8.6327 5.6802 3.2153 9.5393 7.2815 7.1600 11.3087 6.1828 6.8579 9.3617 8.8780 4.6976 3.9478 7.3776

x = min(max(x,1),10) % this is all you need.

x = 5×7

7.6491 8.4519 8.8820 8.7385 9.8065 8.6945 8.5660 5.7131 10.0000 6.3650 9.1859 6.9860 9.4199 5.4750 8.8947 7.3018 6.4618 7.2714 9.2859 8.7553 5.7112 8.6327 5.6802 3.2153 9.5393 7.2815 7.1600 10.0000 6.1828 6.8579 9.3617 8.8780 4.6976 3.9478 7.3776

Answer 2

[Rik]

The problem is that you assume Matlab will process each element of x separately. Matlab will only do that if you use a loop.

An alternative is to use logical indexing to process x as an array.

L=x<1;
x(L)=1;
L=x>10;
x(L)=10;
L=x>3;
x(L)=1.3* x(L) -0.75;

[Ivan Mich]

I am sorry but your solution is no use.. I tried it...

[Rik]

Can you spot why it doesn't work? Can you also see how you could fix it?

The simplest solution would be to create a second array:

L=x<1;
y(L)=1;
L=x>10;
y(L)=10;
L=x>3 & x<10;
y(L)=1.3* x(L) -0.75;

[Ivan Mich]

Because values greater than 10 are shown. This is what I mean

[Rik]

In that case you should use the code Stephen suggested.

If you have a piecewise function you can use the code I suggested.