I think I've got a vague idea what happens here... The same thing also happens when I define the max() function myself:
sage: def my_max(x,y): sage: if(x>y): return x sage: else: return y sage: fermi2(x,y,d,L) = 1 - 1/( exp( ( my_max(abs(x),abs(y))-L) /d) + 1) sage: fermi2 (x, y, d, L) |--> -1/(e^(-(L - abs(y))/d) + 1) + 1 This looks a bit like max(x,y) gets passed the the objects 'abs(x)' and 'abs(y)' and decides, for whatever reason, that 'abs(x)' is not greater than 'abs(y)', so the else-clause gets executed and we are left with abs(y). Does this make sense to you? (I'm just thinking aloud, I got no idea how sage actually does it) Most likely the internal "max" function is defined in rather the same way (it just returns abs(x) instead of abs(y). ) The bottom line seems to be that it is a very dangerous game to mix symbolic expressions and python functions. Is there some way to control when (and how) Sage evaluates expressions and invokes python functions? Something like saying "first evaluate abs(x) and abs(y) and then invoke the python function max() with the result of the evaluation"? On Mar 12, 5:49 pm, Harald Schilly <harald.schi...@gmail.com> wrote: > Ah, I got it, the max function is evaluated during the definition of > the function, look: > > sage: fermi(x,y,d,L) = 1 - 1/( exp( ( max(abs(x),abs(y))-L) /d) + 1) > sage: fermi > (x, y, d, L) |--> -1/(e^(-(L - abs(x))/d) + 1) + 1 > > especially: > sage: max(abs(x),abs(y)) > abs(x) > > There is no y any more! > > H -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
