How to put value in symbolic variable in differential equation (Newton Raphson Method)?
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Mudasir Ahmed
le 3 Mai 2016
Commenté : Walter Roberson
le 15 Mai 2016
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 commentaires
Walter Roberson
le 15 Mai 2016
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
le 15 Mai 2016
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.
Réponse acceptée
Walter Roberson
le 3 Mai 2016
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 commentaire
Walter Roberson
le 5 Mai 2016
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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