[Octave-bug-tracker] [bug #47811] int gives wrong answer in symbolic pkg.

[Doug Stewart]

URL:
  <http://savannah.gnu.org/bugs/?47811>

                 Summary: int gives wrong answer in symbolic pkg.
                 Project: GNU Octave
            Submitted by: dastew
            Submitted on: Sat 30 Apr 2016 12:58:09 GMT
                Category: Octave Forge Package
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Incorrect Result
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.1
        Operating System: Any

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Details:

The answer for the integration of a*b^x   is wrong.
It is probably a bug in the sympy system but I
have not proved that.

The following code demonstrates the error.


## demo of error in symbolic integration.

clear
syms a b x
int(a*b^x)

# when b=1 the log(b) ==> 0
log(1)

# now try one example 
aa=3 
xx=5

bb1=[.9:.001:1];
plot(bb1,aa.*bb1.^xx)
xlabel("value of b")
hold on 

bb1=[1:.001:1.1];
plot(bb1,aa.*bb1.^xx)

hold off

# we can see from the graph that the actual value of y
# when b=1 is 3 the value of a,   not 15 as a*x would be. 






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