Differentiating gives wrong result
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Hello
One of my functions returns this symbolic expression
(10000*(x2*cos((9*pi)/40) + x1*sin((9*pi)/40))^2)/9801 + (10000*(x1*cos((9*pi)/40) - x2*sin((9*pi)/40))^2)/9801 - 1
If I use the diff function(by x1) on it, it gives wrong result(ignores the variables or I don't know):
(20000*cos((9*pi)/40)*(x1*cos((9*pi)/40) - x2*sin((9*pi)/40)))/9801 + (20000*sin((9*pi)/40)*(x2*cos((9*pi)/40) + x1*sin((9*pi)/40)))/9801
Instead of:
(50706024009129175657667733171308125*x1)/24848487065673752728138376231780352
If I simply run this code, it works, so something is probably wrong with my returned expression from the function
syms x1 x2
f=(10000*(x2*cos((9*pi)/40) + x1*sin((9*pi)/40))^2)/9801 + (10000*(x1*cos((9*pi)/40) - x2*sin((9*pi)/40))^2)/9801 - 1;
diff(f,x1)
2 件のコメント
Alex Mcaulley
2019 年 8 月 12 日
Can you show the complete code that generates the symbolic expression? As you say, it works just executing your code.
採用された回答
Alex Mcaulley
2019 年 8 月 12 日
I don't know why the result is presented in different way depending on the case, but the result is allways the same:
%Case 1
syms x1 x2
f = (10000*(x2*cos((9*pi)/40) + x1*sin((9*pi)/40))^2)/9801 + (10000*(x1*cos((9*pi)/40) - x2*sin((9*pi)/40))^2)/9801 - 1;
sol = diff(f,x1)
sol =
(50706024009129175657667733171308125*x1)/24848487065673752728138376231780352
double(subs(sol,x1,1))
ans =
2.0406
%Case 2
syms x1 x2 lambda d1 d2 d3 center1 center2
d1=0.9900;d2=0.9900;d3=9*pi/40;
center1=0;center2=0;
ell = testfunc;
ell = subs(ell);
g = ell;
sol = diff(g,x1)
sol =
(20000*cos((9*pi)/40)*(x1*cos((9*pi)/40) - x2*sin((9*pi)/40)))/9801 + (20000*sin((9*pi)/40)*(x2*cos((9*pi)/40) + x1*sin((9*pi)/40)))/9801
sol = simplify(sol)
sol =
(20000*x1)/9801
double(subs(sol,x1,1))
ans =
2.0406
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