# plpolv

## calculate y-value for an x-value of a polynomial

parametertypeunitsdescription
xfloatuux-value for which polynomial value is to be returned
returns:float

## Description

plpolv returns the value at x of the polynomial calculated earlier by plpoly/plpolf.

## Examples

The following program plot a polynomial and then instructs you how to interpolate on it by hand. The program itself interpolates by using:
```#include <simplot.h>
int main() {
float x[]={1,2,3,4};
float y[]={0,1,4,9};
float xmin=0,xmax=5,ymin=0,ymax=10,xpol=3.5,ypol;

plinit(PS,"plpolv",A4,50,50,"","");
plset(XGRID,TRUE);
plaxes(xmin,ymin,xmax,ymax,100,60,"X","Y","Polynomial interpolation");
plframe(5,3);
plpline(x,y,4,"X",UP);
plclip(xmin,ymin,xmax,ymax);
plpoly(x,y,4,2,xmin,xmax,DOWN);
ypol=plpolv(xpol);
plot(xpol,ymin,UP);
plformat(0,0,"X");
plarrow(0,ypol,5,10,30,FALSE,FALSE,TRUE,FALSE,"");
plot(xpol,ypol,UP);
plformat(0,0,"X");
plarrow(-xpol,0,5,10,30,FALSE,FALSE,TRUE,FALSE,"");
plunclip();
plset(PENDIA,2);
plpscomt("start plframe");
exit(0);
}
```

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