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How to put value in symbolic variable in differential equation (Newton Raphson Method)?

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Mudasir Ahmed
Mudasir Ahmed 2016-5-3
评论： Walter Roberson 2016-5-15
hi
i need help in the following code. i require "df" value in numeric form but here i get the complete expressions due to syms alpha1 alpha2 alpha3. Kindly help me and guide me how i get results of "df" and "inv(df)" in numeric format. kindly help me please :)
with best regards Mudasir
alpha1=0.2;
alpha2=0.4;
alpha3=0.6;
v1desired=10;
T=[v1desired 0 0]';
f1=[ cos(alpha1)+cos(alpha2)+cos(alpha3)
cos(5*alpha1)+cos(5*alpha2)+cos(5*alpha3)
cos(7*alpha1)+cos(7*alpha2)+cos(7*alpha3)];
syms alpha1 alpha2 alpha3
f=[ cos(alpha1)+cos(alpha2)+cos(alpha3)
cos(5*alpha1)+cos(5*alpha2)+cos(5*alpha3)
cos(7*alpha1)+cos(7*alpha2)+cos(7*alpha3)];
df=jacobian(f,[alpha1;alpha2;alpha3])
dalpha=(inv(df))*(T-f1);
  2 个评论
Walter Roberson
Walter Roberson 2016-5-15
Mudasir Ahmed commented
Dear sir, i want to delete this question. because i post here my actual code of research. so i will be highly thankful to you if you delete this question please :) best regards mudasir
Walter Roberson
Walter Roberson 2016-5-15
Musadir, your code contains algorithm that are in common use, nothing new or confidential. We will leave the question so that other people using the same kind of algorithm can learn from it.

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采纳的回答

Walter Roberson
Walter Roberson 2016-5-3
v_alpha1=0.2;
v_alpha2=0.4;
v_alpha3=0.6;
v1desired=10;
T=[v1desired 0 0]';
syms alpha1 alpha2 alpha3
f1 = [ cos(alpha1)+cos(alpha2)+cos(alpha3)
cos(5*alpha1)+cos(5*alpha2)+cos(5*alpha3)
cos(7*alpha1)+cos(7*alpha2)+cos(7*alpha3)];
f = [ cos(alpha1)+cos(alpha2)+cos(alpha3)
cos(5*alpha1)+cos(5*alpha2)+cos(5*alpha3)
cos(7*alpha1)+cos(7*alpha2)+cos(7*alpha3)];
df = jacobian(f,[alpha1;alpha2;alpha3])
dalpha_sym = (inv(df))*(T-f1);
dalpha = double( subs(dalpha_sym, [alpha1, alpha2, alpha3], [v_alpha1, v_alpha2, v_alpha3]));
  1 个评论
Walter Roberson
Walter Roberson 2016-5-5
The inv() will fail when det(df)) is 0. You can solve(det(df),alpha1) and you will be given back a bunch of conditions. For example, the inv() will fail if alpha1 = alpha2. There is nothing you can do about that as long as you continue to use inv(). This is why inv() is not used in real problems.
You should consider substituting in numeric values first and then using pinv() instead of inv()

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