| LUsolve 
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             LUsolve(a, b)  
          or LUsolve(a, b, which=which)  
 	 or a_inverse= LUsolve(a)  
 
     returns the solution x of the matrix equation:  
        A(,+)*x(+) = B  
     If A is an n-by-n matrix then B must have length n, and the returned  
     x will also have length n.  
     B may have additional dimensions, in which case the returned x  
     will have the same additional dimensions.  The WHICH dimension of B,  
     and of the returned x is the one of length n which participates  
     in the matrix solve.  By default, WHICH=1, so that the equations  
     being solved are:  
        A(,+)*x(+,..) = B  
     Non-positive WHICH counts from the final dimension (as for the  
     sort and transpose functions), so that WHICH=0 solves:  
        x(..,+)*A(,+) = B  
     Other examples:  
        A_ij X_jklm = B_iklm   (WHICH=1)  
        A_ij X_kjlm = B_kilm   (WHICH=2)  
        A_ij X_klmj = B_klmi   (WHICH=4 or WHICH=0)  
     If the B argument is omitted, the inverse of A is returned:  
     A(,+)*x(+,) and A(,+)*x(,+) will be unit matrices.  
     LUsolve works by LU decomposition using Gaussian elimination with  
     pivoting.  It is the fastest way to solve square matrices.  QRsolve  
     handles non-square matrices, as does SVsolve.  SVsolve is slowest,  
     but can deal with highly singular matrices sensibly.  
interpreted function, defined at i0/matrix.i   line 106  
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