Compute trig. function in symbolic matrix

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Sam Ade
Sam Ade 2015-10-30
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]

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Walter Roberson
Walter Roberson 2015-10-30
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
Sam Ade
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
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.)

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