• SJSU Singular Matrix Database
  • Matrix group: Regtools
  • Click here for a description of the Regtools group.
  • Click here for a list of all matrices
  • Click here for a list of all matrix groups

  • Matrix: Regtools/tomo_2500
  • Description: TOMO 2500x2500: Create a 2D tomography test problem.
  • download as a MATLAB mat-file, file size: 1 MB. Use SJget(267) or SJget('Regtools/tomo_2500') in MATLAB.
  • download in Matrix Market format, file size: 2 MB.
  • download in Rutherford/Boeing format, file size: 2 MB.


    Routine svd from Matlab (R2008a) used to calculate the singular values.


    Matrix properties (click for a legend)  
    number of rows2,500
    number of columns2,500
    structural full rank?yes
    structural rank2,500
    numerical rank 2,496
    dimension of the numerical null space4
    numerical rank / min(size(A))0.9984
    Euclidean norm of A 55.317
    calculated singular value # 24960.0016308
    numerical rank defined using a tolerance
    max(size(A))*eps(norm(A)) =
    calculated singular value # 24971.21e-015
    gap in the singular values at the numerical rank:
    singular value # 2496 / singular value # 2497
    calculated condition number2.6355e+017
    # of blocks from dmperm1
    # strongly connected comp.1
    entries not in dmperm blocks0
    explicit zero entries0
    nonzero pattern symmetry 3%
    numeric value symmetry 0%
    Cholesky candidate?no
    positive definite?no

    editorPer Christian Hansen
    kindill-posed problem
    2D/3D problem?no

    Additional fieldssize and type
    bfull 2500-by-1
    xfull 2500-by-1


        Constructed by the call [A,b,x]= tomo(50)                            
      where tomo is from Regularization Tools. The description of            
      tomo from http://www2.imm.dtu.dk/~pch/Regutools/ is:                   
                    [A,b,x] = tomo(N,f);                                     
      This function creates a simple two-dimensional tomography test problem.
      A 2D domain [0,N] x [0,N] is divided into N^2 cells of unit size, and a
      total of round(f*N^2) rays in random directions penetrate this domain. 
      The default value is f = 1.                                            
      Each cell is assigned a value (stored in the vector x), and for each   
      ray the corresponding element in the right-hand side b is the line     
      integral along the ray, i.e.                                           
         sum_{cells in ray}  x_{cell j} * length_{cell j}                    
      where length_{cell j} is the length of the ray in the j-th cell.       
      The matrix A is sparse, and each row (corresponding to a ray) holds    
      the value length_{cell j} in the j-th position.  Hence:                
         b = A*x .                                                           
      Once a solution x_reg has been computed, it can be visualized by means 
      of imagesc(reshape(x_reg,N,N)).                                        
      The exact solution, reshape(x,N,N), is identical to the exact image in 
      the function blur.                                                     
      Note that the code for tomo uses random numbers and repeated calls to  
      tomo will produce different matrices.                                  

    Ordering statistics:AMD METIS
    nnz(chol(P*(A+A'+s*I)*P'))2,655,352 2,628,222
    Cholesky flop count4.0e+009 3.9e+009
    nnz(L+U), no partial pivoting5,308,204 5,253,944
    nnz(V) for QR, upper bound nnz(L) for LU2,917,949 2,901,781
    nnz(R) for QR, upper bound nnz(U) for LU3,106,075 3,102,952

    Maintained by Leslie Foster, last updated 24-Apr-2009.

    Entries 5 through 14 in the table of matrix properties and the singular
    value plot were created using SJsingular code. The other plots
    and statistics are produced using utilities from the SuiteSparse package.
    Matrix color plot pictures by cspy, a MATLAB function in the CSparse package.