Help with for loop and invalid expression

Question

Az Naqvi 2021-8-6

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/893407-help-with-for-loop-and-invalid-expression

回答： Dave B 2021-8-6

Hi, I'm currently stuck on this loop and I'm getting an inalid expression error at the moment. Would be greatful if someone could help me resolve it please.

m=458 
n= 2
t = 30
for i=1:m
for j=1:n
    x = 1.4*sin(t^1.6) + 0.3*tan(t^1.3)
    t = t+0.01 
    a(i,j)=(t,x)            %this is where the first error occurs
    
end
end
a=reshape(a,m,n)
figure
hold on
plot(a,Linespace)
title('Displacement vs time')
v = reshape(a,m,n); 
b = reshape(a.m.n) 
for i in x:
    if(x(1,i) >20)
        v = x(1,i)
    else
        b = x(1,i)
    end
end
figure
hold on
plot(v,Linespace,'g')
plot(b,Linespace,'r')
title('Displacement vs time')

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Answer 1

Dave B 2021-8-6

0
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https://ww2.mathworks.cn/matlabcentral/answers/893407-help-with-for-loop-and-invalid-expression#answer_762112

在 MATLAB Online 中打开

The line of code

a(i,j)=(t,x);

doesn't make sense. a(i,j) is a location in a matrix, namely the ith row and jth column of the matrix a. You can only store one value there. So you can do:

a(i,j) = t;

or

a(i,j) = x;

or even

a(i,j,1:2)=[1 2]; % if a was a 3 dimensional matrix

My guess is leave the t out of the loop, it looks like it's something like:

t = 0:.01:(numel(a)-1)*.01;

Once you've done that, you'll realize you can probably leave the assignment of the loop:

a = 1.4.*sin(t.^1.6) + 0.3.*tan(t.^1.3);
% but I'll leave it to you to figure out how big t should be without
% relying on numel(a). It's pretty simple!