Hard crash when multiplying by empty matrix (process exits -1)

[jdanbrown]

import Surge

let X = Matrix<Float>([[1]])
let Y = Matrix<Float>([[]])

print("X")
print(X) // Ok
print("Y")
print(Y) // Ok
print("X*Y")
print(X*Y) // Hard crash

Output:

X
(       1.0     )

Y
(               )

X*Y
ldb must be >= MAX(N,1): ldb=0 N=0ldc must be >= MAX(N,1): ldc=0 N=0BLAS error: Parameter number 11 passed to cblas_sgemm had an invalid value

When run like swift <script>.swift, process prints that error msg and exits -1 (= 255), without printing a stacktrace. When run in Xcode, debugger doesn't activate.

Seems like Surge mul() needs to guard against the rows=0 / columns=0 cases and return an appropriate empty Matrix, instead of letting blas crash?

[alejandro-isaza]

Added a precondition check.

[jdanbrown]

Thanks! But what do you think about returning an empty/zero matrix instead of treating it as an error? That seems less surprising mathematically, since empty matrices are valid objects. That's what e.g. numpy chooses to do:

>>> M = lambda r, c: np.random.rand(r, c)

>>> np.dot(M(1,2), M(2,0))
array([], shape=(1, 0), dtype=float64)

>>> np.dot(M(0,2), M(2,3))
array([], shape=(0, 3), dtype=float64)

>>> np.dot(M(1,0), M(0,3))
array([[0., 0., 0.]])

[alejandro-isaza]

Interesting, what about this: https://github.com/mattt/Surge/pull/93