MATLAB Answers

## Symbolic Math Toolbox VS MuPAD: example in advance of the first?

Asked by Igor

### Igor (view profile)

on 6 Jun 2011
Accepted Answer by Walter Roberson

### Walter Roberson (view profile)

MATLAB
>> simplify(exp(log10(x)))
ans =
x^(1/log(10))
MuPAD
simplify(exp(log(10,x)), ln)
No effect. How to force MuPAD to simplify truely? I used consider MATLAB Simb.Tbx as a reduced version of MuPAD? That is -- MATLAB calls the MuPAD functions...

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## 3 Answers ### Walter Roberson (view profile)

Answer by Walter Roberson

### Walter Roberson (view profile)

on 7 Jun 2011
Accepted Answer

This is as documented here
Mathematically, log(b, b^y) = y holds true for any real y. This simplification is implemented for the following cases: i) b is a symbolic (indexed) identifier and y is of type Type::Real, ii) b is numerical and y is integer or rational.
and
Note that arithmetical rules such as log(b, x*y) = log(b, x) + log(b, y) are not valid throughout the complex plane. Use properties to mark identifiers as real and apply functions such as expand or simplify to manipulate expressions involving log. Cf. example 4.
So you could possibly use
simplify(exp(log(10,x))) assuming x::real

Walter Roberson

### Walter Roberson (view profile)

on 7 Jun 2011
Might have to be x::Real perhaps, instead of x::real
Igor

### Igor (view profile)

on 7 Jun 2011
Clearly.
But Log of complex value may be account like sin() with periodic term.
Thanks.

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Answer by Paulo Silva

### Paulo Silva (view profile)

on 6 Jun 2011

syms x
simplify(exp(log10(x)))

Igor

### Igor (view profile)

on 6 Jun 2011
No, no :)
MATLAB works validly, you haven't seen ANS
Problem in MuPAD

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Answer by Andrei Bobrov

### Andrei Bobrov (view profile)

on 6 Jun 2011

in MuPAD
expand(subs(exp(log(10,x)),log(10,x)=ln(x)/ln(10)));
EDIT
rewrite(exp(log(10,x)),ln)

Igor

### Igor (view profile)

on 7 Jun 2011
the last better..
thanks

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