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| SGEMV/DGEMV/CGEMV/ZGEMV | ||
| y | Array containing the vector y. The number of elements | ||
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| of y and the value of leny, the dimension of the array y, | ||
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| depend on trans: |
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| ’N’ or ’n’ | y has m elements | leny = (m−1)⋅incy+1 |
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| otherwise | y has n elements | leny = (n−1)⋅incy+1 |
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| Not used as input if beta = 0. |
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| incy | Increment for the array y, incy ≠ 0: | ||
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| incy > 0 | y is stored forward in array y; that is, | |
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| yi is stored in y((i−1)⋅incy+1). | |
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| incy < 0 | y is stored backward in array y; that | |
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| is, if trans = ’N’ or ’n’, then yi is stored | |
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| in y((i−m)⋅incy+1); otherwise, yi is | |
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| stored in y((i−n)⋅incy+1). | |
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| Use incy = 1 if the vector y is stored contiguously in | ||
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| array y, that is, if yi is stored in y(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 | y | The updated y vector replaces the input. | ||
Notes These subprograms conform to specifications of the Level 2 BLAS.
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
trans ≠ ’N’ or ’n’ or ’T’ or ’t’ or ’C’ or ’c’ m < 0
n < 0
lda < max(m,1) incx = 0
incy = 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 235