plot real part and imaginary part of function sqrt.

[fmaltey]

I try to plot a half-circle with the

var('m')
parametric_plot ([real(m+sqrt(1-m^2)), imaginary(m+sqrt(1-m^2))],m,-1,1)

and get a severe error.

Theses plots are right :

plot([sqrt(m2+1)],m,0,6)
plot(real (sqrt(m2+1)),m,0,6)

But this one with AND real(...) or imaginary(...) AND list AND sqrt(...) fails :

plot([real (sqrt(m2+1))],m,0,6)

On devel-support kcrisman proposes :

After looking at the traceback about an extra argument, I have a sneaky suspicion this is because sqrt takes an extra keyword prec, which perhaps is getting caught up in fast_float somehow. What's interesting is that the problem also only shows up for a list, so again fast_float([]) is what's getting concerned. Those who know how fast_float and the expression trees work will hopefully check this out as they get an opportunity.

[mhansen]

I've attached a patch which fixes the error you get. However, I don't think that's the right equation to draw a half circle since sqrt(1-m^{2) is always going to be real for -1 <= m <= 1.}

[kcrisman]

Looks good, passes all the tests I can think of.

If it's significant enough that

sage: plot([real (sqrt(m^2-1))],m,0,6)

now works, maybe there should be a doctest in plot/plot.py?

Otherwise positive review.