In doing some stuff with BLAS operations I see the level 1 operation SSWAP.
I can't come up with a programming use case for this.
My thinking is, if you where passing y to a function but wanted it with the values of x, why not simply pass x? Swapping the values seems rather convoluted.
This is just a question out of curiosity.
Sometimes swapping the content of two (stride) vectors is exactly what you need. For instance when doing row or column interchanges in pivoting during LU factorization -- the reference BLAS uses xSWAP in xGBTRF. The pivoting algorithm for LU decomposition requires swapping the content of two rows (or columns). These two rows (or columns) can be thought of as two vectors (possibly with non-unit stride between the elements). One needs to do many such interchanges along the way, and they gradually change, so there is no option to "just send some other line to a function" at the end of the algorithm.
To sum up, as a basic building block of more complex algorithms, a (potentially) optimized routine for interchanging columns or rows of a matrix seems useful.