decimal increment in a for loop

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www 2016-3-17

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/273934-decimal-increment-in-a-for-loop

评论： Star Strider 2016-3-17

Hi all, I have this equation inv(A-z.^2*B)*C where A, B are two by two matrix and C is 2 by 1 matrix. The problem is that I want to run the equation for a range of z variables at an increment of 0.1 or 0.001. So I thought, maybe it would be good to use a for loop.

savedata =[];
for i=1:0.1:500
    z(i)=i
    EQN = inv(A-z(i).^2*B)*C
    datasave = [savedata;EQN(1)]
end

This code however, produce an error 'Subscript indices must either be real positive integers or logicals'. Looking forward for some help!

Thank you in advance.

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Answer 1

Star Strider 2016-3-17

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https://ww2.mathworks.cn/matlabcentral/answers/273934-decimal-increment-in-a-for-loop#answer_213908

在 MATLAB Online 中打开

I am not certain what you are doing.

This will run your loop:

A = randi(9, 2);                                % Create Matrix
B = randi(9, 2);                                % Create Matrix
C = randi(9, 2, 1);                             % Create Vector
z = 1:0.1:500;
for i=1:length(z)
    EQN(:,i) = (A-z(i).^2*B)\C;
end

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www 2016-3-17

Hi Polar bear coder! Thank you again for the help T.T . Because I have a range of z = 1:0.0001:100; ,is there a way to make it run faster and then extract only the data from row 1 and plot it against z?

Star Strider 2016-3-17

在 MATLAB Online 中打开

My pleasure!

I experimented using bsxfun but because ‘z’ is a vector and ‘B’ is (2x2), it is not possible to multiply them except using the loop with element-by-element scalar multiplication in your loop. Replacing your inv call with the mldivide,\ call is the only optimisation I can provide.

Plotting them as you want is straightforward:

A = randi(9, 2);                                % Create Matrix
B = randi(9, 2);                                % Create Matrix
C = randi(9, 2, 1);                             % Create Vector
z = 1:0.1:500;
for i=1:length(z)
    EQN(:,i) = (A-z(i).^2*B)\C;
end
figure(1)
plot(z, EQN(1,:))                               % Plot First Row
grid