# Need help to form equations

3 views (last 30 days)
Sameer on 6 Jun 2014
Edited: Sameer on 6 Jun 2014
Hello all
I want to form the equations through the matlab commands,I have the matrix of constants....Can anyone guide how can I form the equations. Example equations
1) a1v1^2-a2v2-a3v3^2-a4v4=0
2) a3v3^2-a4v4-a1v1=0
3) a1v1+a4v4-a3v3^2=0
4) a2v2+a1v1+a3v3-a4v4=0
where a's are constant and I have a matrix for a and I have to find v's.
I want to use them in fsolve.
Regards

David Sanchez on 6 Jun 2014
a = rand(1,4); % your a matrix
syms v1 v2 v3 v4
S = solve( a(1)*v1^2-a(2)*v2-a(3)*v3^2-a(4)*v4==0,...
a(3)*v3^2-a(4)*v4-a(1)*v1==0,...
a(1)*v1+a(4)*v4-a(3)*v3^2==0,...
a(2)*v2+a(1)*v1+a(3)*v3-a(4)*v4==0)
S =
v1: [4x1 sym]
v2: [4x1 sym]
v3: [4x1 sym]
v4: [4x1 sym]
To display the solutions, access the elements of the structure array S
S.v1
ans =
0
0.76082746713182598996024745838092
- 0.38041373356591299498012372919046 - 0.65889591443313132581875790778993*i
- 0.38041373356591299498012372919046 + 0.65889591443313132581875790778993*i
##### 2 CommentsShowHide 1 older comment
Sameer on 6 Jun 2014
To give the more clear idea:
function F = Equation_trial( x )
F= [50-20*x(1)-30*x(2)-40*x(3);
30*x(2)-50*x(4)-60*x(5);
20*x(1)+60*x(5)-70*x(6);
70*x(6)+50*x(4)+40*x(3)-80*x(7);
50000+20-x(8)-500*x(1)^2;
50000+20-x(9)-500*x(2)^2;
50000+20-x(10)-500*x(3)^2;
500*x(2)^2+x(9)-x(11)-500*x(4)^2;
500*x(2)^2+x(9)-x(12)-500*x(5)^2;
500*x(6)^2+x(13)-x(8)-500*x(1)^2;
500*x(6)^2+x(13)-x(12)-500*x(5)^2;
500*x(7)^2+x(14)-x(10)-500*x(3)^2;
500*x(7)^2+x(14)-x(11)-500*x(4)^2;
500*x(7)^2+x(14)-x(13)-500*x(6)^2];
end
x0=[1,1,1,1,1,1,1,1,1,1,1,1,1,1]'
[x,fval]=fsolve(@Equation_trial,x0)
This is what I have to do but I want these equations to be generated on its own using a loop.
regards