I need to find four coeffecients for the equation y=a-b*exp(-c*x^d). I have
the x and y values but want to smooth the data. I've been trying to fit a
non-linear trend to the equation using the power and log trends but since my
equation differs I cannot get them to work. Do you know any way to find
these coefficients?

Wow, I don't know my trig anymore.
I don't suppose you could fit an explanation of that equiation in 100 words
or less?

" wrote:

I need to find four coeffecients for the equation y=a-b*exp(-c*x^d). I have
the x and y values but want to smooth the data. I've been trying to fit a
non-linear trend to the equation using the power and log trends but since my
equation differs I cannot get them to work. Do you know any way to find
these coefficients?

So we need to find the a,b,c and d coefficients. A is a constant, b is the
intercept, c is the coefficient to exp(-c*x) and d is the power of x. It is
known as the Weibull function. Can linest only be used for the specific
power, log, linear, and polynomial equations?

"Sean Timmons" wrote:

Wow, I don't know my trig anymore.
I don't suppose you could fit an explanation of that equiation in 100 words
or less?

" wrote:

I need to find four coeffecients for the equation y=a-b*exp(-c*x^d). I have
the x and y values but want to smooth the data. I've been trying to fit a
non-linear trend to the equation using the power and log trends but since my
equation differs I cannot get them to work. Do you know any way to find
these coefficients?

Google is our friend here, since you named the function:
http://www.qualitydigest.com/jan99/html/weibull.html

Dave
--
Brevity is the soul of wit.


" wrote:

So we need to find the a,b,c and d coefficients. A is a constant, b is the
intercept, c is the coefficient to exp(-c*x) and d is the power of x. It is
known as the Weibull function. Can linest only be used for the specific
power, log, linear, and polynomial equations?

"Sean Timmons" wrote:

Wow, I don't know my trig anymore.
I don't suppose you could fit an explanation of that equiation in 100 words
or less?

" wrote:

I need to find four coeffecients for the equation y=a-b*exp(-c*x^d). I have
the x and y values but want to smooth the data. I've been trying to fit a
non-linear trend to the equation using the power and log trends but since my
equation differs I cannot get them to work. Do you know any way to find
these coefficients?

Maybe look at the TREND function, since you know your Xs and Ys?
--
Brevity is the soul of wit.


" wrote:

I need to find four coeffecients for the equation y=a-b*exp(-c*x^d). I have
the x and y values but want to smooth the data. I've been trying to fit a
non-linear trend to the equation using the power and log trends but since my
equation differs I cannot get them to work. Do you know any way to find
these coefficients?

I would think very hard about it, then try to design a Solver approach. The
idea is to minimize error of the predicted relationship: vary the four
parameters a-d while minimizing the difference between x-yActual pairs and
x-yPredicted pairs.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
http://PeltierTech.com
_______


"
m wrote in message
...
I need to find four coeffecients for the equation y=a-b*exp(-c*x^d). I
have
the x and y values but want to smooth the data. I've been trying to fit a
non-linear trend to the equation using the power and log trends but since
my
equation differs I cannot get them to work. Do you know any way to find
these coefficients?

I treid using the solver approach and could not get the correct values.
There is no way to manipulate the equation using the linest function?

"Jon Peltier" wrote:

I would think very hard about it, then try to design a Solver approach. The
idea is to minimize error of the predicted relationship: vary the four
parameters a-d while minimizing the difference between x-yActual pairs and
x-yPredicted pairs.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
http://PeltierTech.com
_______


"
m wrote in message
...
I need to find four coeffecients for the equation y=a-b*exp(-c*x^d). I
have
the x and y values but want to smooth the data. I've been trying to fit a
non-linear trend to the equation using the power and log trends but since
my
equation differs I cannot get them to work. Do you know any way to find
these coefficients?

Linest has no facility for estimating so many convoluted parameters. If you
transform your data, you can use LINEST to compute Weibull parameters:

http://www.qualitydigest.com/jan99/html/weibull.html
http://www.duxbury.com/authors/varde...bull_plot.html

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
http://PeltierTech.com
_______


"
m wrote in message
...
I treid using the solver approach and could not get the correct values.
There is no way to manipulate the equation using the linest function?

"Jon Peltier" wrote:

I would think very hard about it, then try to design a Solver approach.
The
idea is to minimize error of the predicted relationship: vary the four
parameters a-d while minimizing the difference between x-yActual pairs
and
x-yPredicted pairs.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
http://PeltierTech.com
_______


"
m wrote in message
...
I need to find four coeffecients for the equation y=a-b*exp(-c*x^d). I
have
the x and y values but want to smooth the data. I've been trying to
fit a
non-linear trend to the equation using the power and log trends but
since
my
equation differs I cannot get them to work. Do you know any way to
find
these coefficients?

Thanks for your help. I'm starting to think that this might not be possible
without using solver. However, when I use solver, the values are not
dependable because solver needs initial parameters. If anyone else has any
ideas please let me know.

Thanks!

"Jon Peltier" wrote:

Linest has no facility for estimating so many convoluted parameters. If you
transform your data, you can use LINEST to compute Weibull parameters:

http://www.qualitydigest.com/jan99/html/weibull.html
http://www.duxbury.com/authors/varde...bull_plot.html

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
http://PeltierTech.com
_______


"
m wrote in message
...
I treid using the solver approach and could not get the correct values.
There is no way to manipulate the equation using the linest function?

"Jon Peltier" wrote:

I would think very hard about it, then try to design a Solver approach.
The
idea is to minimize error of the predicted relationship: vary the four
parameters a-d while minimizing the difference between x-yActual pairs
and
x-yPredicted pairs.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
http://PeltierTech.com
_______


"
m wrote in message
...
I need to find four coeffecients for the equation y=a-b*exp(-c*x^d). I
have
the x and y values but want to smooth the data. I've been trying to
fit a
non-linear trend to the equation using the power and log trends but
since
my
equation differs I cannot get them to work. Do you know any way to
find
these coefficients?

y=a-b*exp(-c*x^d).
I have the x and y values
However, when I use solver, the values are not
dependable because solver needs initial parameters.

Hi. If interested, I got Solver to work with about 30 test points.
I don't have your data, but just note that x must be =0.
For example, with your x^d, if we had a neg x, and d was 3.4:
=POWER(-1.2, 3.4)
then Excel returns #Num! error, as it can't return the Complex number.
On my test data, a,b,c,& d were given small positive values (~1-3)

In general, Solver can not do Least Square fitting.
The nature of your equation may allow the following technique.
Have your column of x & y values (name y values "y")
Have 4 changing cells names a,b,c_, d. (Note name "c" must be "c_" in
Excel)
Initially put something like 1 in each cell.
Next to y, put your equation based on the changing cells. (name it something
like fx)
=a-b*EXP(-c_*x^d)
Next column is the error =y-fx .
Target cell is the Sum of the errors.

Minimize Target
Changing cells: a,b,c_,d
st:
Target =0
fx<y

Check Option "Assume non-Negative"

Again, this should work, but may not work with your particular values of
a,b,c_ & d.
I would be interested if you emailed me your values.
Thanks.
Dana

--
HTH :)
Dana DeLouis
Windows XP & Office 2003


"
m wrote in message
...
Thanks for your help. I'm starting to think that this might not be
possible
without using solver. However, when I use solver, the values are not
dependable because solver needs initial parameters. If anyone else has
any
ideas please let me know.

Thanks!

"Jon Peltier" wrote:

Linest has no facility for estimating so many convoluted parameters. If
you
transform your data, you can use LINEST to compute Weibull parameters:

http://www.qualitydigest.com/jan99/html/weibull.html

http://www.duxbury.com/authors/varde...bull_plot.html

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
http://PeltierTech.com
_______


"
m wrote in message
...
I treid using the solver approach and could not get the correct values.
There is no way to manipulate the equation using the linest function?

"Jon Peltier" wrote:

I would think very hard about it, then try to design a Solver
approach.
The
idea is to minimize error of the predicted relationship: vary the four
parameters a-d while minimizing the difference between x-yActual pairs
and
x-yPredicted pairs.

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
http://PeltierTech.com
_______


"
m wrote in message
...
I need to find four coeffecients for the equation y=a-b*exp(-c*x^d).
I
have
the x and y values but want to smooth the data. I've been trying to
fit a
non-linear trend to the equation using the power and log trends but
since
my
equation differs I cannot get them to work. Do you know any way to
find
these coefficients?