My if statement nestled in for loop isn't working

Question

d c 2017-3-3

0
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https://ww2.mathworks.cn/matlabcentral/answers/327965-my-if-statement-nestled-in-for-loop-isn-t-working

评论： d c 2017-3-4

When i run the following code, it calculates values x and y only for M=3. I want to calculate x and y for each of M=1,2,3.

 %
x(1)=0;
y(1)=1;
for M=1:3
    if M==1
        h=0.01;
    elseif M==2
        h=0.1;
    elseif M==3
        h=0.5;
    end
    N=1/h;
    for i=1:N
        x(i+1)=x(i)+h;
        y(i+1)=y(i)+h*(x(i)+y(i));
    end
end

Also, since M=3 this would imply h=0.5 (and so N=2) and thus x and y would be 1x3 vectors. However, this is not the case; x and y are returned as 1x101 vectors which suggests it is using the value h=0.01. I'm really lost on why this happens, any help would be appreciated.

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Answer 1

GEEVARGHESE TITUS 2017-3-3

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I have just modified the code to get the output, and the final values for different values of M are stored in a cell.

clear all;
for M=1:3
    clear x;
    clear y;
    x(1)=0;
    y(1)=1;
    if M==1
        h=0.01;
    elseif M==2
        h=0.1;
    elseif M==3
        h=0.5;
    end
    N=1/h;
    for i=1:N
        x(i+1)=x(i)+h;
         y(i+1)=y(i)+h*(x(i)+y(i));
    end
    x1{M}=x;
    y1{M}=y;
end