ExpFit
- Updated2023-02-21
- 2 minute(s) read
Advanced Analysis Library Only
AnalysisLibErrType ExpFit (double arrayX[], double arrayY[], ssize_t numberOfElements, double outputArray[], double *amplitude, double *decay, double *meanSquaredError);
Purpose
 |
Note This function has been superseded by ExpFitEx. |
Finds the coefficient values that best represent the exponential fit of the data points (X, Y) using the least squares method. ExpFit obtains the ith element of the output array using the following formula:
Zi = aedXi
| where | a = amplitude |
| d = decay | |
| i = array index |
ExpFit obtains the mean squared error using the following formula:
where numberOfElements is the number of sample points.
ExpFit can perform this operation in place; that is, the input and output arrays can be the same.
Example Code
/* Generate an exponential pattern and find the best exponential fit. */
double x[200], y[200], z[200];
double first, last, a, b, amp, decay, mse;
n;
n = 200;
first = 0.0;
last = 1.99E2;
Ramp (n, first, last, x); /* x[i] = i */
a = 3.5;
b = -2.75;
for (i=0; i<n; i++)
y[i] = a * exp(b*x[i]);
/* Find the best exponential fit in z. */
ExpFit (x, y, n, z, &, &decay, &mse);
|
Note The y values must be all positive or all negative to perform an exponential fit. |
Parameters
| Input | ||
| Name | Type | Description |
| arrayX | double [] | An array whose elements contain the X coordinates of the (X,Y) data sets. |
| arrayY | double [] | An array whose elements contain the Y coordinates of the (X,Y) data sets. |
| numberOfElements | ssize_t | Number of sample points used in the exponential fit operation. |
| Output | ||
| Name | Type | Description |
| outputArray | double [] | Best exponential fit. |
| amplitude | double | Value that best describes the amplitude of the exponential curve. |
| decay | double | Decay value that best describes the exponential curve. |
| meanSquaredError | double | The mean squared error generated by the difference between the fitted curve and the raw data. |
Return Value
| Name | Type | Description |
| status | AnalysisLibErrType | A value that specifies the type of error that occurred. Refer to analysis.h for definitions of these constants. |
Additional Information
Library: Advanced Analysis Library
Include file: analysis.h
LabWindows/CVI compatibility: LabWindows/CVI 3.1 and later