MATLAB Central Newsreader - how to solve a complex equation with symbolic coefficients?

how to solve a complex equation with symbolic coefficients?

Giuseppe — Fri, 21 May 2010 15:35:21 +0000

the equation is like this

solve('y*pi/b0=0.5*log((sqrt(a2+v^2)+v)/(sqrt(a2+v^2)-v))+2*gp/b0*atan(2*gp/b0*(v/sqrt(a2+v^2)))','v')

1. actually I have know the value of the coefficients in the equation, but how to transfer these value before the 'solve' command

2. It can't work out in matlab even if I syms y bo a2 gp in advance

3. if I replace the coefficients with values I could get the result of 'v', but unfortunately it is in a for loop, so I can't stop the program and write the value into the equation for each step

Thanks!

Re: how to solve a complex equation with symbolic coefficients?

Roger Stafford — Fri, 21 May 2010 17:48:05 +0000

"Giuseppe " <motognere@gmail.com> wrote in message <ht697p$l01$1@fred.mathworks.com>...
> the equation is like this
>
> solve('y*pi/b0=0.5*log((sqrt(a2+v^2)+v)/(sqrt(a2+v^2)-v))+2*gp/b0*atan(2*gp/b0*(v/sqrt(a2+v^2)))','v')
>
> 1. actually I have know the value of the coefficients in the equation, but how to transfer these value before the 'solve' command
>
> 2. It can't work out in matlab even if I syms y bo a2 gp in advance
>
> 3. if I replace the coefficients with values I could get the result of 'v', but unfortunately it is in a for loop, so I can't stop the program and write the value into the equation for each step
>
> Thanks!

Have you tried the 'subs' function?

Roger Stafford

Re: how to solve a complex equation with symbolic coefficients?

Walter Roberson — Fri, 21 May 2010 17:56:22 +0000

Giuseppe wrote:
> the equation is like this
>
> solve('y*pi/b0=0.5*log((sqrt(a2+v^2)+v)/(sqrt(a2+v^2)-v))+2*gp/b0*atan(2*gp/b0*(v/sqrt(a2+v^2)))','v')
>
>
> 1. actually I have know the value of the coefficients in the equation,
> but how to transfer these value before the 'solve' command

subs()

Re: how to solve a complex equation with symbolic coefficients?

Steven Lord — Fri, 21 May 2010 19:05:38 +0000

"Giuseppe " <motognere@gmail.com> wrote in message
news:ht697p$l01$1@fred.mathworks.com...
> the equation is like this
>
> solve('y*pi/b0=0.5*log((sqrt(a2+v^2)+v)/(sqrt(a2+v^2)-v))+2*gp/b0*atan(2*gp/b0*(v/sqrt(a2+v^2)))','v')
>
> 1. actually I have know the value of the coefficients in the equation, but
> how to transfer these value before the 'solve' command

Then don't pass your equation in as a string. Pass it in as a symbolic
expression:

% define appropriate symbolic and/or numeric variables above
S =
solve(0.5*log((sqrt(a2+v^2)+v)/(sqrt(a2+v^2)-v))+2*gp/b0*atan(2*gp/b0*(v/sqrt(a2+v^2)))-y*pi/b0)

--
Steve Lord
slord@mathworks.com
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