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Solving equations involving specific elements of matrices. Is this possible on MATLAB?

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Yagnaseni Roy
Yagnaseni Roy 2014-3-24
编辑： Matt J 2014-3-24
So lets say I have 2 matrices A and B. I need to solve 2 eqns involving specific elements of each matrix. e.g. A(1)+B(2)=4; A(1)-B(2)=2.
Is there any way to do this? My efforts with Fsolve and solve have failed. Here's what I've done so far:
function F=myfun(A,B)
F=[A(1)-B(2)-2;
A(1)+B(2)-4];
end
In the command window I typed:
>>A=ones(2,2);
>> B=ones(2,2);
>> [A,B]=fsolve(@myfun,A,B)
I even tried
[A(1),B(1)]=fsolve(@myfun,A(1),B(1))
Neither attempt worked.

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回答（1 个）

Matt J
Matt J 2014-3-24
编辑：Matt J 2014-3-24
Since the equations are linear, you should just use MLDIVIDE
x = [1 -1; 1 +1]\[2;4]
A(1)=x(1);
B(2)=x(2);
  2 个评论
Yagnaseni Roy
Yagnaseni Roy 2014-3-24
This is just a simplified version (kind of a schematic representation) of the set of equations I'm trying to solve which are actually extremely complicated and non-linear!
Matt J
Matt J 2014-3-24
编辑：Matt J 2014-3-24
If you were to solve the linear equations in your example with FSOLVE, it would look like this
function F=myfun(z)
F = [1 -1; 1 +1]*z(:) - [2;4]
end
and then something like,
z=fsolve(@myfun,[1,1]);
If you then want the solution variables, z(i), placed inside specific matrix entries, you are free to do so by direct assignment, e.g.,
A(1,1)=z(1);
B(2,1)=z(2);

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