Hello, I've got the problem. Can any one help me with that error?

Question

Pablo Alonso 2023-1-24

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1899370-hello-i-ve-got-the-problem-can-any-one-help-me-with-that-error

回答： Walter Roberson 2023-1-24

syms x(t)
D3x = diff(x, t, 3);
D2x = diff(x, t, 2);
Dx = diff(x, t);
eqn = diff(x, t, 2)+2*diff(x, t)+x == 2;
cond = [x(0)==0, diff(x, t)==0];
xSol(t) = dsolve (eqn,cond)

Warning: Number of equations greater than number of indeterminates. Trying heuristics to reduce to square system.

> In symengine

In mupadengine/evalin_internal

In mupadengine/feval_internal

In dsolve>mupadDsolve (line 334)

In dsolve (line 203)

Error using mupadengine/feval_internal

Unable to reduce to square system because the number of equations differs from the number of indeterminates.

Error in dsolve>mupadDsolve (line 334)

T = feval_internal(symengine,'symobj::dsolve',sys,x,options);

Error in dsolve (line 203)

sol = mupadDsolve(args, options);

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Answer 1

Walter Roberson 2023-1-24

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1899370-hello-i-ve-got-the-problem-can-any-one-help-me-with-that-error#answer_1154910

在 MATLAB Online 中打开

cond = [x(0)==0, diff(x, t)==0];

The first part of that sets a boundary condition. The second part of it says that the derivative of x(t) is zero, which is a second equation rather than a boundary condition. The only way to satisfy diff(x, t) == 0 is if x(t) is constant

You probably wanted Dx(0)==0 or similar