symbolic calculation

Why do I get

>> a = sqrt(sym(2))

a =

                                      1/2
                                     2

instead of

a = 2^(1/2)

And I got >> H = sym(hilb(2))

H =

                   [       1.            0.500000000000000]
                   [                                      ]
                   [0.500000000000000    0.333333333333333]

instead of the fraction version. Is there any expert who can tell me how to set this? I use the mathlab 2010b.

Answer 1

[Walter Roberson]

For the first point, try turning off pretty printing

evalin(symengine, 'PRETTYPRINT := FALSE');

I do not promise that it will work, though. If it doesn't, then

char(a)

should show you the linear form.

I don't know why the decimal form is given for the hilbert matrix. You could try, though,

evalin(symengine, 'linalg::hilbert(2)');

See the documentation

[jack]

Hmm, I don't know why I got the following when I tried your suggestion.

>> evalin(symengine, 'PRETTYPRINT := FALSE')

??? Undefined function or variable 'symengine'.

and

evalin(symengine, 'linalg::hilbert(2)')

??? Undefined function or variable 'symengine'.

[jack]

I was wondering that if there is a way for converting between the decimal and the fraction forms for the "symbol" case I mentioned in the question.

[Walter Roberson]

Which Matlab version are you using? If you are using a version old enough that it uses Maple instead of MuPad, then as best I recall sym() did not automatically convert to rational back then (but I could be wrong.)

If you have the Maple engine, try

maple( subs('convert(H,rational)','H', hilb(2)) )

[jack]

The version I used is MATLAB 7.11.0.584(R2010b). I still got

>> maple( subs('convert(H,rational)','H', hilb(2)) )

ans =

[ 1. 0.500000000000000000]

[ ]

[0.500000000000000000 0.333333333333333315]

I find that I don't have the symbolic math toolbox in my matlab. Maybe this is the reason.

[Walter Roberson]

2010b cannot use Maple. If it doesn't know symengine, the implication would be that you do not have the symbolic toolbox, except then I would have expected it to fail on sym . I'm surprised you are getting anywhere with those commands if you don't have the symbolic toolbox.

[jack]

Hmm, that's the key point. Everything will be OK with the symbolic toolbox.

Answer 2

[jack]

The key point is that the MATLAB one uses needs to have the symbolic toolbox. Otherwise, one can not go further for the symbolic calculation.