Putting symbolic array into matrix

Question

Ramses Young 2022-4-29

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1707925-putting-symbolic-array-into-matrix

回答： Walter Roberson 2022-4-29

Hello,

I am trying to take a symbolic variable and subtract it from every value in an array (of some 1xn size) and then solve for this unknown variable later, but I am having trouble seemingly getting the symbolic array to nest correctly.

Here is an example of what I am trying to do,

syms q0
Vy=[300 500 300]
q(1,:)=[q0-(Vy.*2.*4./8)]

After this, q(i,:) will be in a for loop that will use this symbolic variable.

I keep getting an error and I dont know how to modify this in a way where I can still solve for q0 later on.

Thanks for the help!!!

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Answer 1

Walter Roberson 2022-4-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1707925-putting-symbolic-array-into-matrix#answer_953560

在 MATLAB Online 中打开

That code works in the form you posted.

syms q0

Vy=[300 500 300]

Vy = 1×3

300 500 300

q(1,:)=[q0-(Vy.*2.*4./8)]

q =

The most common mistake for something like that would have been to initialize q using zeros(), such as

q = zeros(5,3);

If you had initialized q to double precision, then the assigning into q(1,:) would fail because what you are assigning needs to contain a symbolic variable.

The cure for that would be to use something like

q = zeros(5, 3, 'sym');

for new enough versions of MATLAB, or

q = sym(zeros(5,3));

if your MATLAB is older than that.