# MATLAB: Replace diagonals in a matrix

mathematicsMATLABmatlab functionmatricesmatrixmatrix arraysolve

Hello every one,
How to replace the upper and lower part of a n*n matrix with zeros (The upper part starts from "diagonal+2" until n while the lower part starts from "diagonal-2" until n)?

For example,
A=rand(10),A = 10×10    0.3632    0.5683    0.2698    0.2133    0.4828    0.8948    0.0478    0.7711    0.5088    0.7301
0.8024    0.1100    0.1475    0.6313    0.8957    0.8629    0.1435    0.8356    0.1381    0.8203
0.8949    0.0767    0.3939    0.2073    0.3055    0.5721    0.7656    0.1443    0.3270    0.6013
0.5722    0.1502    0.8491    0.7124    0.9746    0.7291    0.9774    0.9558    0.4083    0.0934
0.1948    0.7491    0.7331    0.3686    0.4528    0.2436    0.2373    0.4254    0.9163    0.6997
0.4224    0.4079    0.6316    0.8894    0.8130    0.2013    0.0054    0.5217    0.1405    0.7939
0.0219    0.5942    0.3860    0.2447    0.6384    0.9649    0.3000    0.2048    0.2233    0.1450
0.4361    0.2666    0.2646    0.3323    0.6236    0.6866    0.9302    0.3413    0.4398    0.0531
0.3450    0.6491    0.0609    0.1894    0.8414    0.7489    0.1080    0.4159    0.2769    0.3304
0.0411    0.9652    0.9593    0.3298    0.9979    0.3895    0.2349    0.0686    0.9871    0.3078
mask=tril(  triu(  true(size(A)), -2  ), +2);B=A.*maskB = 10×10    0.3632    0.5683    0.2698         0         0         0         0         0         0         0
0.8024    0.1100    0.1475    0.6313         0         0         0         0         0         0
0.8949    0.0767    0.3939    0.2073    0.3055         0         0         0         0         0
0    0.1502    0.8491    0.7124    0.9746    0.7291         0         0         0         0
0         0    0.7331    0.3686    0.4528    0.2436    0.2373         0         0         0
0         0         0    0.8894    0.8130    0.2013    0.0054    0.5217         0         0
0         0         0         0    0.6384    0.9649    0.3000    0.2048    0.2233         0
0         0         0         0         0    0.6866    0.9302    0.3413    0.4398    0.0531
0         0         0         0         0         0    0.1080    0.4159    0.2769    0.3304
0         0         0         0         0         0         0    0.0686    0.9871    0.3078