Compute trig. function in symbolic matrix

Question

Sam Ade 2015-10-30

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/251807-compute-trig-function-in-symbolic-matrix

评论： Walter Roberson 2015-10-30

Hi,

I have a symbolic matrix (as shown below). I would like for matlab to compute the trig functions with non-th5 values. How do I go about this.

Thanks in advance.

[         cos(th5),        -sin(th5),        0, 0]
[ cos(90)*sin(th5), cos(90)*cos(th5), -sin(90), 0]
[ sin(90)*sin(th5), sin(90)*cos(th5),  cos(90), 0]
[                0,                0,        0, 1]

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2015-10-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/251807-compute-trig-function-in-symbolic-matrix#answer_197890

在 MATLAB Online 中打开

Are you referring to reducing the sin(90) and cos(90) to the corresponding constant values? Because if you are then you need to take into account that sin() and cos() operate in radians, not in degrees. But this is your purpose then vpa() the symbolic matrix.

If you are wanting to substitute a numeric value for th5 then use subs(), possibly in conjunction with vpa() or double()

subs(TheMatrix, th5, 1.238343) %put in a particular numeric value

2 个评论
显示无隐藏无

Sam Ade 2015-10-30

编辑：Sam Ade 2015-10-30

Hi, thank you for your answer. I was hoping I could compute the trig. functions in degrees while still keeping the other symbolic trig. functions so I can reduce the matrix. I mean to have something like this [ cos(th5) -sin(th5) 0 0; 0 0 -1 0;sin(th5) cos(th5) 0 0;0 0 0 1]

Walter Roberson 2015-10-30

You can call sind() or cosd() in a symbolic expression, provided it is at the MATLAB level (not in a string that has been passed to solve() or the like.)

请先登录，再进行评论。