SAPYB for BlockDataContainer

[samdporter]

In order to work with other code (e.g SVRGFunction) BlockDataContainer.sapyb method needs to be able to accept out=None and should return a BlockDataContainer

    def sapyb(self, a, y, b, out, num_threads = NUM_THREADS):
        r'''performs axpby element-wise on the BlockDataContainer containers'''
        if out is None:
            out = self*0 
        kwargs = {'a':a, 'b':b, 'out':out, 'num_threads': NUM_THREADS}
        return self.binary_operations(BlockDataContainer.SAPYB, y, **kwargs)

Currently throws error in SVRG.approximate_gradient

[MargaretDuff]

Thanks @samdporter

Yep, that would be a quick fix to currently not allowing the user to pass None to out:

CIL/Wrappers/Python/cil/framework/block.py

Lines 286 to 312 in 5d569dc

	def sapyb(self, a, y, b, out, num_threads = NUM_THREADS):
	r'''performs axpby element-wise on the BlockDataContainer containers
	Does the operation .. math:: a*x+b*y and stores the result in out, where x is self
	:param a: scalar
	:param b: scalar
	:param y: compatible (Block)DataContainer
	:param out: (Block)DataContainer to store the result
	Example:
	--------
	>>> a = 2
	>>> b = 3
	>>> ig = ImageGeometry(10,11)
	>>> x = ig.allocate(1)
	>>> y = ig.allocate(2)
	>>> bdc1 = BlockDataContainer(2*x, y)
	>>> bdc2 = BlockDataContainer(x, 2*y)
	>>> out = bdc1.sapyb(a,bdc2,b)
	'''
	if out is None:
	raise ValueError("out container cannot be None")
	kwargs = {'a':a, 'b':b, 'out':out, 'num_threads': NUM_THREADS}
	self.binary_operations(BlockDataContainer.SAPYB, y, **kwargs)

Will chat to the team about any checks we might need or if they can remember the thinking in the first place