MATLAB Central Newsreader - syms and vpa problem

Re: syms and vpa problem

Fri, 10 Aug 2007 12:24:32 -0400

On Aug 8, 10:25 am, "Steven Lord" <sl...@mathworks.com> wrote:
> "P" <prashanthr...@gmail.com> wrote in message
>
> news:1186548206.565623.216510@k79g2000hse.googlegroups.com...
>
>
>
> > On Aug 7, 9:48 pm, "Steven Lord" <sl...@mathworks.com> wrote:
> >> "P" <prashanthr...@gmail.com> wrote in message
>
> >>news:1186516859.503046.118710@22g2000hsm.googlegroups.com...
>
> >> > Hi all,
>
> >> > I have a variable called
>
> >> > sym_dPhi =
> >> > -282270057375923/2361183241434822606848*cos(phis
> >> > +2835403426559781/1125899906842624)-5849622991223293/18889465931478580854784*cos(phis
> >> > +1649123417284613/281474976710656)+8867307977828847/75557863725914323419136*cos(phis
> >> > +1667188769632673/281474976710656)-6776253911855553/18889465931478580854784*cos(phis
> >> > +5867111522062989/9007199254740992)+7154406299740559/75557863725914323419136*cos(phis
> >> > +6355945788037667/1125899906842624)
>
> >> > where phis is created as syms phis.
>
> >> > vpa(sym_dyPhi,5) yields me
> >> > ans =
>
> >> > [ empty sym ]
>
> >> > Why ?
>
> >> Do you have a typo in your command or in your posting? In the first
> >> output,
> >> your variable is named sym_dPhi, while in your command it's sym_dyPhi.
> >> If
> >> you had a variable named sym_dyPhi that was empty, VPA would return an
> >> empty
> >> sym. Alternately, if the line in this posting has a typo and you're
> >> actually computing vpa(sy_dPhi, 5), what is phis at the time you call
> >> VPA?
>
> >> --
> >> Steve Lord
> >> sl...@mathworks.com
>
> > Hi Steve,
>
> > Thanks for replying !
>
> > Sorry about my initial post. I guarantee no typos in my script.
>
> > when I call "phis", its still a sym ... meaning I have not substituted
> > at value. I do that in the next step using subs(sym_dyPhi,some_value).
>
> > What next ?
>
> I think you're going to need to post:
>
> the content of the sym_dyPhi variable
> the content of the phis variable
> the value you're substituting into sym_dyPhi
> the output of "subs(sym_dyPhi, <the value you're substituting in>)"
>
> --
> Steve Lord
> sl...@mathworks.com

SOLVED THE MYSTERY !

Rather than providing more on this ... let me tell you guys, when this
happens ! IT happens when MATLAB stops the execution of my code and
goes to some wierd state. I am not able to call or use many functions
examples of which include vpa, subs, tic ... toc etc.

It gives me a wrong error ! It says my code is erroneous but I would
not agree with that cause in a different machine with different
version, the script runs fine !

http://groups.google.com/group/comp.soft-sys.matlab/browse_thread/thread/4ac1bcb548e064e1/3124207eb0564fcb#3124207eb0564fcb

That new post is the new problem I am facing related to this !

Thanks to all !
Super Thanks !
P

Re: syms and vpa problem

Steven Lord — Wed, 08 Aug 2007 14:25:07 -0400

"P" <prashanthramu@gmail.com> wrote in message
news:1186548206.565623.216510@k79g2000hse.googlegroups.com...
> On Aug 7, 9:48 pm, "Steven Lord" <slord@mathworks.com> wrote:
>> "P" <prashanthramu@gmail.com> wrote in message
>>
>> news:1186516859.503046.118710@22g2000hsm.googlegroups.com...
>>
>>
>>
>> > Hi all,
>>
>> > I have a variable called
>>
>> > sym_dPhi =
>> > -282270057375923/2361183241434822606848*cos(phis
>> > +2835403426559781/1125899906842624)-5849622991223293/18889465931478580854784*cos(phis
>> > +1649123417284613/281474976710656)+8867307977828847/75557863725914323419136*cos(phis
>> > +1667188769632673/281474976710656)-6776253911855553/18889465931478580854784*cos(phis
>> > +5867111522062989/9007199254740992)+7154406299740559/75557863725914323419136*cos(phis
>> > +6355945788037667/1125899906842624)
>>
>> > where phis is created as syms phis.
>>
>> > vpa(sym_dyPhi,5) yields me
>> > ans =
>>
>> > [ empty sym ]
>>
>> > Why ?
>>
>> Do you have a typo in your command or in your posting? In the first
>> output,
>> your variable is named sym_dPhi, while in your command it's sym_dyPhi.
>> If
>> you had a variable named sym_dyPhi that was empty, VPA would return an
>> empty
>> sym. Alternately, if the line in this posting has a typo and you're
>> actually computing vpa(sy_dPhi, 5), what is phis at the time you call
>> VPA?
>>
>> --
>> Steve Lord
>> slord@mathworks.com
>
> Hi Steve,
>
> Thanks for replying !
>
> Sorry about my initial post. I guarantee no typos in my script.
>
> when I call "phis", its still a sym ... meaning I have not substituted
> at value. I do that in the next step using subs(sym_dyPhi,some_value).
>
> What next ?

I think you're going to need to post:

the content of the sym_dyPhi variable
the content of the phis variable
the value you're substituting into sym_dyPhi
the output of "subs(sym_dyPhi, <the value you're substituting in>)"

--
Steve Lord
slord@mathworks.com

Re: syms and vpa problem

Wed, 08 Aug 2007 04:43:26 -0400

On Aug 7, 9:48 pm, "Steven Lord" <slord@mathworks.com> wrote:
> "P" <prashanthramu@gmail.com> wrote in message
>
> news:1186516859.503046.118710@22g2000hsm.googlegroups.com...
>
>
>
> > Hi all,
>
> > I have a variable called
>
> > sym_dPhi =
> > -282270057375923/2361183241434822606848*cos(phis
> > +2835403426559781/1125899906842624)-5849622991223293/18889465931478580854784*cos(phis
> > +1649123417284613/281474976710656)+8867307977828847/75557863725914323419136*cos(phis
> > +1667188769632673/281474976710656)-6776253911855553/18889465931478580854784*cos(phis
> > +5867111522062989/9007199254740992)+7154406299740559/75557863725914323419136*cos(phis
> > +6355945788037667/1125899906842624)
>
> > where phis is created as syms phis.
>
> > vpa(sym_dyPhi,5) yields me
> > ans =
>
> > [ empty sym ]
>
> > Why ?
>
> Do you have a typo in your command or in your posting? In the first output,
> your variable is named sym_dPhi, while in your command it's sym_dyPhi. If
> you had a variable named sym_dyPhi that was empty, VPA would return an empty
> sym. Alternately, if the line in this posting has a typo and you're
> actually computing vpa(sy_dPhi, 5), what is phis at the time you call VPA?
>
> --
> Steve Lord
> slord@mathworks.com

Hi Steve,

Thanks for replying !

Sorry about my initial post. I guarantee no typos in my script.

when I call "phis", its still a sym ... meaning I have not substituted
at value. I do that in the next step using subs(sym_dyPhi,some_value).

What next ?

Thanks,
P

Re: syms and vpa problem

Steven Lord — Wed, 08 Aug 2007 01:48:34 -0400

"P" <prashanthramu@gmail.com> wrote in message
news:1186516859.503046.118710@22g2000hsm.googlegroups.com...
> Hi all,
>
> I have a variable called
>
> sym_dPhi =
> -282270057375923/2361183241434822606848*cos(phis
> +2835403426559781/1125899906842624)-5849622991223293/18889465931478580854784*cos(phis
> +1649123417284613/281474976710656)+8867307977828847/75557863725914323419136*cos(phis
> +1667188769632673/281474976710656)-6776253911855553/18889465931478580854784*cos(phis
> +5867111522062989/9007199254740992)+7154406299740559/75557863725914323419136*cos(phis
> +6355945788037667/1125899906842624)
>
> where phis is created as syms phis.
>
> vpa(sym_dyPhi,5) yields me
> ans =
>
> [ empty sym ]
>
> Why ?

Do you have a typo in your command or in your posting? In the first output,
your variable is named sym_dPhi, while in your command it's sym_dyPhi. If
you had a variable named sym_dyPhi that was empty, VPA would return an empty
sym. Alternately, if the line in this posting has a typo and you're
actually computing vpa(sy_dPhi, 5), what is phis at the time you call VPA?

--
Steve Lord
slord@mathworks.com

Re: syms and vpa problem

Wed, 08 Aug 2007 01:23:41 -0400

On Aug 7, 6:48 pm, "us " <u...@neurol.unizh.ch> wrote:
> P:
> <SNIP has a very simple variable precision arithmetic: it's
> simply always empty...
>
> here (r2007a) your example yields
>
> syms phis
> s=...
> -282270057375923/2361183241434822606848*...
> cos(phis+2835403426559781/1125899906842624)-...
> 5849622991223293/18889465931478580854784*...
> cos(phis+1649123417284613/281474976710656)+...
> 8867307977828847/75557863725914323419136*...
> cos(phis+1667188769632673/281474976710656)...
> -6776253911855553/18889465931478580854784*...
> cos(phis+5867111522062989/9007199254740992)...
> +7154406299740559/75557863725914323419136*...
> cos(phis+6355945788037667/1125899906842624);
> vpa(s,1)
> % -.1e-6*cos(phis+3.)-.1e-6*cos(phis+6.)-.4e-6*cos(phis+.7)
>
> us

Thanks ! Really dont know whats going wrong here !

I am running ...

MATLAB Version 7.3.0.298 (R2006b)
Operating System: Linux 2.6.18-8.1.1.el5 #1 SMP Mon Feb 26 20:37:57
EST 2007 x86_64

Re: syms and vpa problem

us — Tue, 07 Aug 2007 22:48:22 -0400

P:
<SNIP has a very simple variable precision arithmetic: it's
simply always empty...

here (r2007a) your example yields

syms phis
s=...
-282270057375923/2361183241434822606848*...
     cos(phis+2835403426559781/1125899906842624)-...
5849622991223293/18889465931478580854784*...
     cos(phis+1649123417284613/281474976710656)+...
8867307977828847/75557863725914323419136*...
     cos(phis+1667188769632673/281474976710656)...
-6776253911855553/18889465931478580854784*...
     cos(phis+5867111522062989/9007199254740992)...
+7154406299740559/75557863725914323419136*...
     cos(phis+6355945788037667/1125899906842624);
vpa(s,1)
% -.1e-6*cos(phis+3.)-.1e-6*cos(phis+6.)-.4e-6*cos(phis+.7)

us

Re: syms and vpa problem

ellieandrogerxyzzy@mindspring.com.invalid (Roger Stafford) — Tue, 07 Aug 2007 22:30:17 -0400

In article <1186516859.503046.118710@22g2000hsm.googlegroups.com>, P
<prashanthramu@gmail.com> wrote:

> Hi all,
>
> I have a variable called
>
> sym_dPhi =
> -282270057375923/2361183241434822606848*cos(phis
>
+2835403426559781/1125899906842624)-5849622991223293/18889465931478580854784*cos(phis
>
+1649123417284613/281474976710656)+8867307977828847/75557863725914323419136*cos(phis
>
+1667188769632673/281474976710656)-6776253911855553/18889465931478580854784*cos(phis
>
+5867111522062989/9007199254740992)+7154406299740559/75557863725914323419136*cos(phis
> +6355945788037667/1125899906842624)
>
> where phis is created as syms phis.
>
> vpa(sym_dyPhi,5) yields me
> ans =
>
> [ empty sym ]
>
> Why ?
>
>
> On a parallel line ...
>
> >> syms B
> >> syms c; B = 1 + pi + c
>
> B =
> 1165754695714211/281474976710656+c
>
> >> vpa(B,2)
> ans =
> 4.1+c
>
> Works !
>
> How come ? What am I doing wrong ? Any suggestions ?
>
> Thanks,
> ethnicatom
----------------------
With my ancient version of matlab (4a), 'sym' variables are simply
strings. When I copy your string with its five cosine functions into a
single long string on the command line to define a symbolic variable,
matlab complains that it can't see the end of the string. When I break it
up into five separate command line strings and then concatenate them into
a single string, it works fine. The answer is:

vpa(f,5)

ans =

-.11955e-6*cos(phis+2.5183)-.30968e-6*cos(phis+5.8589)+.11736e-6*cos(phis+5.9230)-.35873e-6*cos(phis+.65138)+.94688e-7*cos(phis+5.6452)

So, at least in my case, the trouble seems to be due to the allowable
length of the command line string, not the length of string matlab's Maple
can handle. It seems possible that your trouble may also be due to some
such limitation on the command line string length, even if your Symbolic
Toolbox itself may be very different from mine.

Roger Stafford

Re: syms and vpa problem

Tue, 07 Aug 2007 20:02:18 -0400

On Aug 7, 4:00 pm, P <prashanthr...@gmail.com> wrote:
> Hi all,
>
> I have a variable called
>
> sym_dPhi =
> -282270057375923/2361183241434822606848*cos(phis
> +2835403426559781/1125899906842624)-5849622991223293/18889465931478580854784*cos(phis
> +1649123417284613/281474976710656)+8867307977828847/75557863725914323419136*cos(phis
> +1667188769632673/281474976710656)-6776253911855553/18889465931478580854784*cos(phis
> +5867111522062989/9007199254740992)+7154406299740559/75557863725914323419136*cos(phis
> +6355945788037667/1125899906842624)
>
> where phis is created as syms phis.
>
> vpa(sym_dyPhi,5) yields me
> ans =
>
> [ empty sym ]
>
> Why ?
>
> On a parallel line ...
>
> >> syms B
> >> syms c; B = 1 + pi + c
>
> B =
> 1165754695714211/281474976710656+c
>
> >> vpa(B,2)
>
> ans =
> 4.1+c
>
> Works !
>
> How come ? What am I doing wrong ? Any suggestions ?
>
> Thanks,
> ethnicatom

please note even vpa(sym_dyPhi,25) yields me no answer !

syms and vpa problem

Tue, 07 Aug 2007 20:00:59 -0400

Hi all,

I have a variable called

sym_dPhi =
-282270057375923/2361183241434822606848*cos(phis
+2835403426559781/1125899906842624)-5849622991223293/18889465931478580854784*cos(phis
+1649123417284613/281474976710656)+8867307977828847/75557863725914323419136*cos(phis
+1667188769632673/281474976710656)-6776253911855553/18889465931478580854784*cos(phis
+5867111522062989/9007199254740992)+7154406299740559/75557863725914323419136*cos(phis
+6355945788037667/1125899906842624)

where phis is created as syms phis.

vpa(sym_dyPhi,5) yields me
ans =

[ empty sym ]

Why ?

On a parallel line ...

>> syms B
>> syms c; B = 1 + pi + c

B =
1165754695714211/281474976710656+c

>> vpa(B,2)
ans =
4.1+c

Works !

How come ? What am I doing wrong ? Any suggestions ?

Thanks,
ethnicatom