MATLAB: Retrieve coefficients from multivariable symbolic equation.

symbolic

Hi,

what will be the easiest/best to extract coefficients from multivariate symbolic equations. for instance if I have

131823*c1^4 - 1092957*c1^3*c2 - 1903326*c1^3*c3 + 315414*c1^3 + 681399*c1^2*c2^2 + 291012*c1^2*c2*c3 - 642874*c1^2*c2 + 97275*c1^2*c3^2 + 3458345*c1^2*c3 + 124940*c1^2 + 560571*c1*c2^3 + 1107126*c1*c2^2*c3 + 149922*c1*c2^2 + 548367*c1*c2*c3^2 + 342112*c1*c2*c3 + 457357*c1*c2 + 2496438*c1*c3^3 + 330818*c1*c3^2 - 657587*c1*c3 - 82147*c1 + 779506*c2^3 - 2672451*c2^2*c3 - 254337*c2^2 + 69082*c2*c3^2 + 76916*c2*c3 + 50604*c2 - 1760499*c3^3 - 800417*c3^2 - 317442*c3 - 22910

How can I extract – 800417 as the coefficient of c3^2 and 681399 as the coefficient of c1^2*c2^2?

Thanks

Best Answer

Hi,

I think the coeffs function from the Symbolic Math Toolbox could help here:

http://www.mathworks.com/help/releases/R2011a/toolbox/symbolic/coeffs.html

Related Solutions

MATLAB: Solve symbol four equations for c1 c2 c3 c4

Thanks, I solve it,

clc
clear
syms a b x y c1 c2 c3 c4 T1 T2 T3 T4  
T=c1+c2*x+c3*y+c4*x*y;
%%
r1=c1+c2*a+c3*b+c4*a*b-T1;
r2=c1-c2*a+c3*b-c4*a*b-T2;
r3=c1-c2*a-c3*b+c4*a*b-T3;
r4=c1+c2*a-c3*b-c4*a*b-T4;
%%Find C1 and C4
p13=r1+r3;
p24=r2+r4;
n1=solve(p13==0,c1);
n2=solve(p24==0,c1);
C4=solve(n1==n2,c4)
w1=solve(p13==0,c4);
w2=solve(p24==0,c4);
C1=solve(w1==w2,c1)
r1=subs(r1,c1,C1);
r1=subs(r1,c4,C4);
r2=subs(r2,c1,C1);
r2=subs(r2,c4,C4);
r3=subs(r3,c1,C1);
r3=subs(r3,c4,C4);
r4=subs(r4,c1,C1);
r4=subs(r4,c4,C4);
%%Find C3
q12=r1+r2;
q34=r3+r4;
C3=solve(q12==0,c3)
r1=subs(r1,c3,C3);
r2=subs(r2,c3,C3);
r3=subs(r3,c3,C3);
r4=subs(r4,c3,C3);
%% find C2
C2=solve(r1==0,c2)
r1=subs(r1,c2,C2);
r2=subs(r2,c2,C2);
r3=subs(r3,c2,C2);
r4=subs(r4,c2,C2);
C1
C2
C3
C4

MATLAB: Replacing variables with dumthe variables

The only one that I can think of is the Symbolic Math Toolbox coeffs (link) function. Others, such as simplify (link), and related functions linked to on that page, could also be useful.

Best Answer

Related Solutions

MATLAB: Solve symbol four equations for c1 c2 c3 c4

MATLAB: Replacing variables with dumthe variables

Related Question