Wilfried_Huss wrote:
>
>
> On 19 Mrz., 18:49, Jason Grout <jason-s...@creativetrax.com> wrote:
>> Jason Grout wrote:
>>> Wilfried_Huss wrote:
>>>> On 19 Mrz., 16:47, Jason Grout <jason-s...@creativetrax.com> wrote:
>>>>> ma...@mendelu.cz wrote:
>>>>>> Hello, this command produces one half of a cirle, not 1/4 as excepted.
>>>>>> I think that this is a bug in sage 3.4
>>>>>> Robert
>>>>>> region_plot([y>0,x>0,x^2+y^2<3], (-3, 3), (-3,
>>>>>> 3),plot_points=100,incol='gray').show(aspect_ratio=1)
>>>>> I get a quarter-circle on my sage 3.4 and on sagenb.org. Can you try on
>>>>> sagenb.org?
>>>> This works:
>>>> sage: var('x,y')
>>>> sage: region_plot([y>0,x>0,x^2+y^2<3], (x, -3, 3), (y, -3,3))
>>>> But if one leaves out the variables, one gets an half circle:
>>>> sage: region_plot([y>0,x>0,x^2+y^2<3], (-3, 3), (-3,3))
>>>> I've written a patch which fixes this:
>>>> http://trac.sagemath.org/sage_trac/ticket/5567
>>> Ah, yes, good catch. For those that want to know, Sage was interpreting
>>> the first two constraints as functions of one variable, so when it
>>> plugged in two numbers, Sage behaved as though you had typed x>0, x>0.
>>> When I did my example, I explicitly put in the variable names (it's a
>>> good habit to be explicit in plotting), so I got the right plot.
>>> There should be a standard function that takes a tuple of functions and
>>> returns a list of variables for all the functions. This is used all
>>> over the plotting code, the fast_callable code, now this code, etc.
>>> Basically, there should be a function that, treating a tuple of
>>> functions as a vector-valued function, returns the variables used in the
>>> vector-valued function.
>>> Also, I wonder why fast_float is not used? It could drastically speed
>>> up plots. You could just replace the lines like:
>>> s = symbolic_expression(f.rhs() - f.lhs()).function(*variables)
>>> with
>>> s = fast_float(f.rhs() - f.lhs(), *vars)
>>> and you'd probably see at least an order of magnitude speedup. (make
>>> sure to do "from sage.ext.fast_eval import fast_float" first).
>> Actually, I believe that the call to setup_eval_on_grid automatically
>> does the call to fast_float, so it's probably already happening and we
>> don't have to worry about anything.
>
> Yes
>
>> In fact, I think the root of the problem is in
>> plot/plot3d/parametric_plot3d.py in the adapt_to_callable function (this
>> is called by setup_for_eval_on_grid, which is in turn called by
>> region_plot). Observe (and please pardon my debugging in public :)
>>
>> sage: from sage.plot.plot3d.parametric_plot3d import adapt_to_callable
>> sage: var('x,y')
>> (x, y)
>> sage: funcs = [x,y]
>> sage: adapt_to_callable(funcs,2)
>>
>> ((<sage.ext.interpreters.wrapper_rdf.Wrapper_rdf object at 0xa9b1d9c>,
>> <sage.ext.interpreters.wrapper_rdf.Wrapper_rdf object at 0xa9d916c>),
>> (y, x))
>>
>> First of all, why in the world are the arguments y, then x? I thought
>> the convention was alphabetical ordering if an ordering wasn't specified.
>>
>> Well, the problem is in this line of adapt_to_callable:
>>
>> tuple(sorted(set(sum( [z.variables() for z in f], ()) )))
>>
>> Note:
>>
>> sage: sorted(set(sum([z.variables() for z in funcs],())))
>> [y, x]
>>
>> and even
>>
>> sage: sorted(list(set(sum([z.variables() for z in funcs],()))))
>> [y, x]
>>
>> For some reason, sorting the list [y,x] doesn't make it [x,y]:
>>
>> sage: sorted([y,x])
>> [y, x]
>
> Well, that is not surprising since x < y is a symbolic equation.
> We need to sort the variables by name.
>
> sage: sorted([y,x], cmp = lambda a,b: cmp(repr(a), repr(b)) )
> [x, y]
>
> But, fixing the variable order in adapt_to_callable does not
> solve the problem in region_plot, because setup_for_eval_on_grid
> calls adapt_to_callable in a loop for one function at a time.
>
Ah, I see that; right.. So maybe the problem is in
setup_for_eval_on_grid after all.
Carl Witty and I have been discussing this on IRC too. Soon, we hope
that adapt_to_callable (and part of setup_for_eval_on_grid) is made
obsolete by fast_callable. Until that makes it into Sage, though, this
probably ought to be fixed.
Do you have time to fix setup_for_eval_on_grid? It would probably be a
similar fix to the one you made in region_plot.
Jason
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