Syntax

[C/C++:]
void ggReturnLineCoeffs(int type, int npts, GPOINT *points, int ncoef, float coeffs[ ], int *nmax, int *er);

[F90:]
subroutine ggReturnLineCoeffs(type, npts, points, ncoef, coeffs, nmax, er)

integer, intent(in) :: type, npts, ncoef
integer, intent(out) :: nmax, er
type(GPOINT), intent(in) :: points(*)
real, intent(out) :: coeffs(*)

Arguments

type
Type of line fitting performed on the data set

= GLEASTSQUARE

Least squares straight line fit

> 1	Reserved for future use

points
Array of dimension npts, giving the X and Y axis values of the points defined on the graph

npts
The number of points in X and Y

ncoef
The number of coefficients required to be returned

coeffs
Array of dimension ncoef, returning the coefficients of the fitted line

nmax
The total number of coefficients of the fitted line

= 0,	No coefficients returned due to argument or fitting error

> 0,	Number of coefficients of successful fit

er
Error flag

= GSUCCESS

Successful fit

= GFAIL

Unsuccessful fit

Description

The routine ggReturnLineCoeffs() takes a set of data points and fits a straight line or curve to it, returning their coefficients to the user. No graphics output is generated by this routine.

The data is supplied in the components points.x, points.y each having npts points. The coefficients are returned in the array coeffs which should have the same dimension as the number of coefficients required as set in ncoef. The actual number of coefficients calculated by the fitting algorithm is returned in nmax which may be more or less than ncoef.

In the case of the straight line fit (type=GLEASTSQUARE), the two coefficients 'a' and 'b' of line 'y=ax + b' are returned in coeffs(2) and coeffs(1) respectively.

If less than two points are supplied or less that one coefficient is requested, an error message is generated and no fitting is attempted. If there is enough data but a fit is not possible (ie, if the points are located in one position, or if all the points have the same Y coordinate values) the error flag er is set to 1 but no error message is produced. In either of these cases nmax is set to zero to indicate that no coefficients have been returned.

See Also

ggReturnLineCoeffs Usage

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