Seems like there is a potential for unexpected results here.  But, from the point of view of a developer, having the LHS fixed does make it easier.

Matlab does allow assigning of integers to sparse arrays.  I'm not that bothered about implementing it because I think this is probably a low-probability coding event that can always be solved by casting to double on the part of the programmer.

Marking the bug as fixed since the issue with floats has been dealt with.  Up to you whether you want to also implement integer assignment.

Closing report.

This is expected.  Sparse matrices are only implemented for double values.

Is the expectation that the single value will be automatically converted to double?  This is what Matlab does, but I don't like that it does it without any sort of warning.

The normal rules for mathematical operations are that the result type is most restrictive possible.  So when combining singles with doubles the result is of type single.  And when combining integers with floating point the result is of type integer.

octave:5> x = double (1)
x = 1
octave:6> class (x)
ans = double
octave:7> x = x + single (2)
x = 3
octave:8> class (x)
ans = single
octave:9> x = x + uint8 (3)
x = 6
octave:10> class (x)
ans = uint8

Neither Matlab nor Octave allow the creation of a single sparse matrices.  It seems to me that an error is appropriate.  This forces the programmer to add a call to double() around the assigned value thereby reminding them that calculations will occur with doubles going forward.

As per comment 16 in https://savannah.gnu.org/bugs/?60818

octave:1> a=sparse(1)
a = Compressed Column Sparse (rows = 1, cols = 1, nnz = 1 [100%])

  (1, 1) -> 1
octave:octave:1> a=sparse(1)
a = Compressed Column Sparse (rows = 1, cols = 1, nnz = 1 [100%])

  (1, 1) -> 1
octave:2> a(1) = single(20)
error: operator =: no conversion for assignment of 'float scalar' to indexed 'sparse matrix'
2> a(1) = single(20)
error: operator =: no conversion for assignment of 'float scalar' to indexed 'sparse matrix'

This is both with 6.2.93 and with current dev tip.

Dmitri.
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