Scilab Function
Last update : 23/10/2007

interp1 - one_dimension interpolation function

Calling Sequence

[yp]=interp1(x, y,xp [, method,[extrapolation]])

Parameters

Description

Given (x,y,xp) , this function performs the yp components corresponding to xp by the interpolation(linear by default) defined by x and y.

If yp is a vector then the length of xp is equal to the length of yp, if yp is a matrix then xp have the same length than the length of each columns of yp, if yp is a hypermatrix then the length of xp have the same length than the first dimension of yp.

If size(y)=[C,M1,M2,M3,...,Mj] and size(xp)=[N1,N2,N3,...,Nk] then size(yp)=[N1,N2,..,Nk,M1,M2,...Mj] and length of x must be equal to size(y,1)

The method parameter sets the evaluation rule for interpolation

  • "linear" : the interpolation is defined by linear method (see interpln )
  • "spline" : the interpolation is defined by cubic spline interpolation ( see splin , interp )
  • "nearest" : for each value xp(j), yp(j) takes the value or y(i) corresponding to x(i) the nearest neighbor of xp(j)

    • The extrapolation parameter sets the evaluation rule for extrapolation, i.e for xp(i) not in [x1,xn] interval

  • "extrap" : the extrapolation is performed by the defined method. yp=interp1(x,y,xp,method,"extrap")
  • real value : you can choose a real value for extrapolation, in this way yp(i) takes this value for xp(i) not in [x1,xn] interval, for example 0 (but also nan or inf). yi=interp1(x,y,xp,method, 0)
  • by default : the extrapolation is performed by the defined method (for spline method), and by nan for linear and nearest methods. yp=interp1(x,y,xp,method)

    • Examples 

    x=linspace(0,3,20);
y=x^2;
xx=linspace(0,3,100);
yy1=interp1(x,y,xx,'linear');
yy2=interp1(x,y,xx,'spline');
yy3=interp1(x,y,xx,'nearest');
plot(xx,[yy1;yy2;yy3],x,y,'*')
xtitle('interpolation of square function')
legend(['linear','spline','nearest'],a=2)

    See Also

    interp ,   interpln ,   splin ,  

    Author

    F.B