solving system of non linear equations using fsolve by converting symbolic expressions

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Ari Dillep Sai
Ari Dillep Sai 2021-11-5
评论： Walter Roberson 2021-11-6
Hi. I want to solve a system of non linear equations in 3 variables using fsolve. But the equations which i get would be in the symbolic form. My code somewhat looks like this:
%file to create equations
syms c d e x;
R=(1+(1-c-d-e+c*x^2+d*x^3+e*x^4))*(2*c+6*d*x+12*e*x^2) + (2*c*x+3*d*x^2+4*e*x^3)^2 -(1-c-d-e+c*x^2+d*x^3+e*x^4);
eq_1=int(R*x^3,x,0,1);
eq_2=int(R*x^2,x,0,1);
eq_3=int(R*x,x,0,1);
Now, I want to solve above equations using fsolve. for that i have created a separate function file, to where i copy the three equations from the command window after running this script file. what i want to know is that, is there any way to update these three equations automatically directly to the function file which i have created.
  2 个评论
Matt J
Matt J 2021-11-5
编辑：Matt J 2021-11-5
First of all, they don't seem to be equations because they are not set equal to anything. Do you intend to set them equal to zero?
Secondly, eq_1 and eq_2 are identical.
Walter Roberson
Walter Roberson 2021-11-6
Symbolic toolbox recognizes pure expressions with no equality in them, as implicit equality with 0. This allows you to easily do things like E = lhs(eq_1) - rhs(eq_1); fplot(E); solve(E) %solutions are places where E is 0

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采纳的回答

Sulaymon Eshkabilov
Ran in:
Here is the solution:
syms c d e x;
R=(1+(1-c-d-e+c*x^2+d*x^3+e*x^4))*(2*c+6*d*x+12*e*x^2) + (2*c*x+3*d*x^2+4*e*x^3)^2 -(1-c-d-e+c*x^2+d*x^3+e*x^4);
eq(1)=int(R*x^3,x,0,1);
eq(2)=int(R*x^3,x,0,1);
eq(3)=int(R*x^2,x,0,1);
SOL = solve(eq==0);
c = double(SOL.c)
c =
1.0e+02 * 0.0000 + 0.0000i 0.0000 + 0.0000i 0.0022 + 0.0000i -0.0369 - 0.0472i -0.0369 + 0.0472i 2.6212 + 0.0000i
d = double(SOL.d)
d =
1.0e+02 * 1.1092 + 0.0000i -0.2601 + 0.0000i -0.0001 + 0.0000i 0.0303 + 0.0183i 0.0303 - 0.0183i -2.2801 + 0.0000i
e = double(SOL.e)
e = 6×1
-214.8882 18.1132 0 0 0 0

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