Solve triangular system |
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| STRSV/DTRSV/CTRSV/ZTRSV |
| incx | Increment for the array x, incx ≠ 0: | |
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| incx > 0 | x is stored forward in array x; that is, |
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| xi is stored in x((i−1)⋅incx+1). |
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| incx < 0 | x is stored backward in array x; that |
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| is, xi is stored in x((i−n)⋅incx+1). |
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| Use incx = 1 if the vector x is stored contiguously in | |
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| array x, that is, if xi is stored in x(i). Refer to “BLAS | |
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| Indexing Conventions” in the introduction to | |
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| Chapter 2. |
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Output | x | The solution vector of the triangular system replaces | |
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| the input. |
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Notes These subprograms conform to specifications of the Level 2 BLAS.
The subprograms do not check for singularity of matrix A. A is singular if diag = ’N’ or ’n’ and some aii = 0. This condition causes a division by zero to occur.
Therefore, the program must detect singularity and take appropriate action to avoid a problem before calling any of these subprograms.
If an error in the arguments is detected, the subprograms call error handler XERBLA, which writes an error message onto the standard error file and terminates execution. The standard version of XERBLA (refer to the end of this chapter) can be replaced with a
uplo ≠ ’L’ or ’l’ or ’U’ or ’u’
trans ≠ ’N’ or ’n’ or ’T’ or ’t’ or ’C’ or ’c’ diag ≠ ’N’ or ’n’ or ’U’ or ’u’
n < 0
lda < max(n,1) incx = 0
Actual character arguments in a subroutine call can be longer than the corresponding dummy arguments. Therefore, readability of the CALL statement may be improved by coding the trans argument as ’NORMAL’ or ’NONTRANS’ for ’N’, ’TRANSPOSE’ for ’T’, or ’CTRANS’ for ’C’. Refer to “Example 2.”
Chapter 3 Basic Matrix Operations 335