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Thread Subject:
solve error function

Subject: solve error function

From: kawak

Date: 24 Jan, 2010 03:10:05

Message: 1 of 5

Hi,

Once again, I need your help :-).

I have got a simple equation : 2*10^-6=erfc(x) with Matlab, where erfc is the the complementary error function.

I would like to solve this equation, so I tried:

y=solve('2*10^-6-erfc(x)','x')

but it doesn't work :

??? Error using ==> solve at 77
' 2*10^-6-erfc(x) ' is not a valid
expression or equation.

Do you have an idea in order to solve this equation without initial conditions?

Thank you

Benjamin

Subject: solve error function

From: kawak

Date: 24 Jan, 2010 03:22:03

Message: 2 of 5

"kawak " <kbenjamin@hotmail.fr> wrote in message <hjgdmd$6t6$1@fred.mathworks.com>...
> Hi,
>
> Once again, I need your help :-).
>
> I have got a simple equation : 2*10^-6=erfc(x) with Matlab, where erfc is the the complementary error function.
>
> I would like to solve this equation, so I tried:
>
> y=solve('2*10^-6-erfc(x)','x')
>
> but it doesn't work :
>
> ??? Error using ==> solve at 77
> ' 2*10^-6-erfc(x) ' is not a valid
> expression or equation.
>
> Do you have an idea in order to solve this equation without initial conditions?
>
> Thank you
>
> Benjamin

I apologize, I found the solution :it's
x=erfcinv(2*10^-6)

sorry for my post...

see you soon ;)

Benjamin

Subject: solve error function

From: Walter Roberson

Date: 24 Jan, 2010 05:17:56

Message: 3 of 5

kawak wrote:
> Hi,
>
> Once again, I need your help :-).
>
> I have got a simple equation : 2*10^-6=erfc(x) with Matlab, where erfc
> is the the complementary error function.
>
> I would like to solve this equation, so I tried:
>
> y=solve('2*10^-6-erfc(x)','x')
>
> but it doesn't work :
>
> ??? Error using ==> solve at 77
> ' 2*10^-6-erfc(x) ' is not a valid
> expression or equation.


The operator ^ cannot be followed by the operator - .
Try solving '2*10^(-6)-erfc(x)'

By the way, it appears the x is imaginary. I don't know if you will be
able to find an exact symbolic value for it.

Subject: solve error function

From: kout supcom

Date: 16 Mar, 2010 10:23:05

Message: 4 of 5

"kawak " <kbenjamin@hotmail.fr> wrote in message <hjgdmd$6t6$1@fred.mathworks.com>...
> Hi,
>
> Once again, I need your help :-).
>
> I have got a simple equation : 2*10^-6=erfc(x) with Matlab, where erfc is the the complementary error function.
>
> I would like to solve this equation, so I tried:
>
> y=solve('2*10^-6-erfc(x)','x')
>
> but it doesn't work :
>
> ??? Error using ==> solve at 77
> ' 2*10^-6-erfc(x) ' is not a valid
> expression or equation.
>
> Do you have an idea in order to solve this equation without initial conditions?
>
> Thank you
>
> Benjamin

Subject: solve error function

From: kout supcom

Date: 16 Mar, 2010 10:27:10

Message: 5 of 5

"kawak " <kbenjamin@hotmail.fr> wrote in message <hjgecr$kv2$1@fred.mathworks.com>...
> "kawak " <kbenjamin@hotmail.fr> wrote in message <hjgdmd$6t6$1@fred.mathworks.com>...
> > Hi,
> >
> > Once again, I need your help :-).
> >
> > I have got a simple equation : 2*10^-6=erfc(x) with Matlab, where erfc is the the complementary error function.
> >
> > I would like to solve this equation, so I tried:
> >
> > y=solve('2*10^-6-erfc(x)','x')
> >
> > but it doesn't work :
> >
> > ??? Error using ==> solve at 77
> > ' 2*10^-6-erfc(x) ' is not a valid
> > expression or equation.
> >
> > Do you have an idea in order to solve this equation without initial conditions?
> >
> > Thank you
> >
> > Benjamin
>
> I apologize, I found the solution :it's
> x=erfcinv(2*10^-6)
>
> sorry for my post...
>
> see you soon ;)
>
> Benjamin

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