abs(pi+I) = pi+I

[sagetrac-benreynwar]

abs(pi+I) returns pi+I

one would have expected:

sqrt(pi^2+1)

Apply attachment: trac_11155-doctest.patch

Depends on #12950

CC: @burcin

Component: symbolics

Author: Alexei Sheplyakov, Titus Nicolae

Reviewer: Burcin Erocal

Merged: sage-5.1.beta4

Issue created by migration from https://trac.sagemath.org/ticket/11155

[kcrisman]

comment:1

In the future, be sure to pick a component (for instance, calculus or symbolics); that will help people find it more easily. Thanks for the bug report; mathematically incorrect is definitely bad!

I can confirm this. Moving to major.

Note the following.

sage: abs(pi+i)
pi + I
sage: abs(1+i)
sqrt(2)
sage: abs(n(pi)+i)
3.29690830947562

Pynac is somehow missing this. Note that it gets e right.

sage: abs(e+i)
abs(e + I)

[williamstein]

Description changed:

--- 
+++ 
@@ -1,4 +1,7 @@
 abs(pi+I) returns pi+I
 
 one would have expected:
+
+```
 sqrt(pi^2+1)
+```

[williamstein]

comment:2

I can confirm this further. It's mathematically seriously incorrect... so now moving from major to critical, and cc'ing burcin.

Note:

sage: z = pi + i
sage: abs(z)
pi + I
sage: sqrt((z*z.conjugate()).expand())
sqrt(pi^2 + 1)

[burcin]

comment:3

Reported to the ginac-devel list:

http://thread.gmane.org/gmane.comp.mathematics.ginac.devel/1363

More detailed about the problem are in my message linked above.

[kcrisman]

comment:4

Apparently already fixed!

[kcrisman]

comment:5

Here is the diff.

diff --git a/check/exam_numeric.cpp b/check/exam_numeric.cpp
index 715acff..d5ae27b 100644 (file)
--- a/check/exam_numeric.cpp
+++ b/check/exam_numeric.cpp
@@ -68,6 +68,11 @@ static unsigned exam_numeric1()
                     << " erroneously not recognized as complex rational" << endl;
                ++result;
        }
+       if (test_crat.info(info_flags::nonnegative)) {
+               clog << test_crat
+                    << " erroneously recognized as non-negative number" << endl;
+               ++result;
+       }
        
        int i = numeric(1984).to_int();
        if (i-1984) {
diff --git a/ginac/numeric.cpp b/ginac/numeric.cpp
index f05763d..18725b2 100644 (file)
--- a/ginac/numeric.cpp
+++ b/ginac/numeric.cpp
@@ -700,7 +700,7 @@ bool numeric::info(unsigned inf) const
                case info_flags::negative:
                        return is_negative();
                case info_flags::nonnegative:
-                       return !is_negative();
+                       return is_zero() || is_positive();
                case info_flags::posint:
                        return is_pos_integer();
                case info_flags::negint: