fix #13309: return correct real value from var, varm, etc of complex arrays #13348
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This fixes issue #13309:
var(iterable)
andvarm(iterable, mean)
were giving the wrong values for complex arraysvar(z)
andvarm(z,mean)
,cov(z)
etc. were giving the correct values, but were suboptimal because they often returned a complex result even though the variance is (by definition) purely realvarm
was type unstable (sometimes returning real, sometimes returning complex results, depending on the length of the complex array)cor(z)
was going to a lot of effort just to return 1. Also, there seems no point in returning a complex or floating-point 1 whenone(real(T))
will do for an array ofT
.