solving two equations with 4 unknowns

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Bahareh
Bahareh 2011-7-7
回答： SooShiant 2014-2-20
Hello all,
Can you please tell me how can I solve 4 equations with 2 unknowns in MATLAB?
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Sean de Wolski
Sean de Wolski 2011-7-7
How is this urgent? Is it going to cure Cancer, end world hunger/tyranny, get us out of work early on this gorgeous Thursday, anything?

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Sean de Wolski
Sean de Wolski 2011-7-7
Edited: Walk before you run:
syms x y
results = solve('3*x+y=9','x-7*y=-3',x,y)
results.x
results.y
look at
doc solve
to learn more.
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Bahareh
Bahareh 2011-7-7
can you please explain your last sentence more?

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更多回答（2 个）

Walter Roberson
Walter Roberson 2011-7-16
syms T12 T11 T21 T22 R11 R12 R21 R22 H21_1 H21_2 H12_1 H12_2 lambda beta alpha
solve((T21.^2.* H21_1.^2+beta^(-1) ).* R11.^2+(T21.* T2_2.* H21_1.* H21_2 ) .*R11.* R12 - (lambda*alpha).*((R21.^2.* H12_1.^2+lambda).* T11.^2+(R21.* R22 H12_1.* H12_2 ).* T11.* T12 ), lambda)
Notice that the A=B form you had has been replaced by A-B, which solve will interpret as indicating that (A-B)=0 is desired.
In the second line, replace the "lambda" at the end by the name of the variable you want to solve for. As you only have one equation, you can only effectively solve for a single variable.
SooShiant
SooShiant 2014-2-20
Combine 2 equation to gain 1 then use this way:
Here is a simple example which you can change the equation and range and solve yours. The equation is 12x+9y+7z-60=0 where x,y,z are integers varies 0 to 10:
x=[0:1:10];
y=[0:1:10];
z=[0:1:10];
[X,Y,Z]=ndgrid(x,y,z);
F=12.*X+9.*Y+7.*Z-60;
idx=find(F==0);
[X(idx(:)),Y(idx(:)),Z(idx(:))];
Equations of this type are known as Diophantine equations.

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