# [TIB] help!! ti-89

Thank you all for answering my previous questions
In the following programm I use the FDM (finite difference method) to calculate the voltage in a net of a particular shape.
I don't know how to solve the system of linear equations
If you any idea please tell me!
Here is the code
fdm()
Prgm
ClrIO
Request "Mx=",mx,0
Request "Nx=",nx,0
Request "My=",my,0
Request "Ny=",ny,0
Request "internal V",v1,0
Request "external V",v2,0
expr(v1)»v1
expr(v2)»v2
expr(mx)»mx
expr(nx)»nx
expr(my)»my
expr(ny)»ny
For i,1,nx
1»j
v1»#("f"&string(i)&"_"&string(j))
EndFor
For j,1,ny
1»i
v1»#("f"&string(i)&"_"&string(j))
EndFor
For i,mx,nx
my»j
v2»#("f"&string(i)&"_"&string(j))
EndFor
For j,my,ny
mx»i
v1»#("f"&string(i)&"_"&string(j))
EndFor
For j,1,my
nx-1»i
#("f"&string(i)&"_"&string(j))»#("f"&string(i+2)&"_"&string(j))
EndFor
For i,1,mx
ny-1»j
#("f"&string(i)&"_"&string(j))»#("f"&string(i)&"_"&string(j+2))
EndFor
For i,2,nx
For j,2,my-1
(#("f"&string(i+1)&"_"&string(j))+#("f"&string(i-1)&"_"&string(j))+#("f"&string(i)&"_"&string(j+1))+#("f"&string(i)&"_"&string(j-1)))/4=#("f"&string(i)&"_"&string(j))»#("eqa"&string(i)&"_"&string(j)):Disp #("eqa"&string(i)&"_"&string(j)):Pause
EndFor
EndFor
For i,2,mx-1
For j,my,ny
(#("f"&string(i+1)&"_"&string(j))+#("f"&string(i-1)&"_"&string(j))+#("f"&string(i)&"_"&string(j+1))+#("f"&string(i)&"_"&string(j-1)))/4=#("f"&string(i)&"_"&string(j))»#("eqb"&string(i)&"_"&string(j)):Disp #("eqb"&string(i)&"_"&string(j)):Pause
EndFor
EndFor
eqa2_2»bool1
For i,2,nx
For j,2,my-1
string(bool1)&" and "&"eqa"&string(i)&"_"&string(j)»bool1
expr(bool1)»bool1
EndFor
EndFor
#("eqb2_"&string(my))»bool2
For i,2,mx-1
For j,my,ny
string(bool2)&" and "&"eqb"&string(i)&"_"&string(j)»bool2
expr(bool2)»bool2
EndFor
EndFor
solve(bool1 and bool2,???????????)»sol
disp sol
pause
EndPrgm
The difficult part is with the question marks.
Please note tha nx>mx and ny>my

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