typesetting
Fix ADI stencils: we do not take the average as in CN
fix stencil: correct misplaced \Delta t
correct ADI linear equations and use correct \sigma
write indices in y-direction from top to bottom
copy and paste correct lineary system for x-direction family
write indices in y-direction in expected order
add matplotlib inline directive
correct \sigma constants
correct f vector
f needs to be multiplied by dt/2