>> % This is the Matlab diary from CS 240A, April 5, 2010
>> % To reproduce this, run in a directory that contains file "temperature.mat"

>> load temperature
>> whos
  Name          Size                Bytes  Class     Attributes

  A100      10000x10000            635204  double    sparse    
  A4           16x16                 2048  double              
  b100      10000x1                 80000  double              
  b4           16x1                   128  double              

>> A4
A4 =
  Columns 1 through 14
     4    -1     0     0    -1     0     0     0     0     0     0     0     0     0
    -1     4    -1     0     0    -1     0     0     0     0     0     0     0     0
     0    -1     4    -1     0     0    -1     0     0     0     0     0     0     0
     0     0    -1     4     0     0     0    -1     0     0     0     0     0     0
    -1     0     0     0     4    -1     0     0    -1     0     0     0     0     0
     0    -1     0     0    -1     4    -1     0     0    -1     0     0     0     0
     0     0    -1     0     0    -1     4    -1     0     0    -1     0     0     0
     0     0     0    -1     0     0    -1     4     0     0     0    -1     0     0
     0     0     0     0    -1     0     0     0     4    -1     0     0    -1     0
     0     0     0     0     0    -1     0     0    -1     4    -1     0     0    -1
     0     0     0     0     0     0    -1     0     0    -1     4    -1     0     0
     0     0     0     0     0     0     0    -1     0     0    -1     4     0     0
     0     0     0     0     0     0     0     0    -1     0     0     0     4    -1
     0     0     0     0     0     0     0     0     0    -1     0     0    -1     4
     0     0     0     0     0     0     0     0     0     0    -1     0     0    -1
     0     0     0     0     0     0     0     0     0     0     0    -1     0     0
  Columns 15 through 16
     0     0
     0     0
     0     0
     0     0
     0     0
     0     0
     0     0
     0     0
     0     0
     0     0
    -1     0
     0    -1
     0     0
    -1     0
     4    -1
    -1     4

>> b4
b4 =
   100
   100
   100
   100
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
     0
>> t= A4 \ b4
t =
   45.4545
   59.4697
   59.4697
   45.4545
   22.3485
   32.9545
   32.9545
   22.3485
   10.9848
   17.0455
   17.0455
   10.9848
    4.5455
    7.1970
    7.1970
    4.5455
>> reshape(t,4,4)
ans =
   45.4545   22.3485   10.9848    4.5455
   59.4697   32.9545   17.0455    7.1970
   59.4697   32.9545   17.0455    7.1970
   45.4545   22.3485   10.9848    4.5455

>> whos
  Name          Size                Bytes  Class     Attributes

  A100      10000x10000            635204  double    sparse    
  A4           16x16                 2048  double              
  T           100x100               80000  double              
  ans           4x4                   128  double              
  b100      10000x1                 80000  double              
  b4           16x1                   128  double              
  t            16x1                   128  double              

>> A100
A100 = 
         (1,1)              4
         (2,1)             -1
       (101,1)             -1
         ...
     (10000,10000)          4

>> spy(A100)

>> t = A100 \ b100;
>> size(t)
ans =
       10000           1
>> t
t =
   49.9893
   69.7438
   79.0289
     ...
    0.0107

>> T = reshape(t,100,100);
>> size(T)
ans =
   100   100

>> surfc(T),shg