interp1

Name

interp1 — one_dimension interpolation function

Calling Sequence

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

Parameters

xp: reals scalar, vector or matrix (or hypermatrix)
x: reals vector
method: (optional) string defining the interpolation method
extrapolation: (optional) string, or real value defining the yp(j) components for xp(j) values outside [x1,xn] interval.
yp: vector, or matrix (or hypermatrix)

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)

Authors

F.B