% data for Exercise Set 2.3
      
ex = input('Exercise number (5-16, 19-20)? ');
      
if ex==5
   M = [1 -5 9 0;-1 4 -3 0;2 -8 9 0]  
elseif ex==6
   M = [3 6 -4 -1 0;-5 0 8 3 0;8 -1 0 7 0]  
elseif ex==7
   M = [5 -1 3 0;4 -3 7 0]  
elseif ex==8
   M = [4 -2 0;6 3 0] 
elseif ex==9
   M = [1 -3 -2 0;0 1 -1 0;-2 3 7 0]  
elseif ex==10
   M = [1 2 -7 0;-2 -3 9 0;0 -2 10 0]  
elseif ex==11
   A = [1 -2 -5 5;0 0 -3 2]
   disp('You could row reduce A and pretend that an extra column of zeros is')
   disp('  augmented to it, but this leads to errors if you forget what you are')
   disp('  doing.  A safer procedure is to augment A with an actual column of zeros')
   disp('  and then row reduce.  Since A has only 2 rows, a MATLAB command that')
   disp('  works is:     M = [A  [0;0]]')
   disp('  Another is:   M = [A  zeros(2,1)]')
   disp('In general,  zeros(m,n)  constructs an m-by-n matrix of zeros.')  
elseif ex==12 
   A = [1 5 16 7;0 2 6 3]
   disp('Try Exercise 11 first, and read the comments about augmenting a matrix')
   disp('  with a column of zeros.') 
elseif ex==13
   A = [1 -5 0 2 0 -4;0 0 0 1 0 -3;0 0 0 0 1 5;0 0 0 0 0 0]  
elseif ex==14 
   A = [1 6 0 8 -1 -2;0 0 1 -3 4 6;0 0 0 0 0 1;0 0 0 0 0 0]  
elseif ex==15
   A = [2 -8 6]  
elseif ex==16
   A = [1 -5 0 4] 
elseif ex==19
   M = [1 -3 -2 -5;0 1 -1 4;-2 3 7 -2] 
elseif ex==20
   M = [1 2 -7 0;-2 -3 9 4;0 -2 10 -8]  
else
   disp('No data for this exercise in Section 2.3.')  
end
