interp1

one_dimension interpolation function

Calling Sequence

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

Arguments

: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)

See Also

• `interp`_ cubic spline evaluation function
• `interpln`_ linear interpolation
• `splin`_ cubic spline interpolation

History

Version Description 5.4.0 previously, imaginary part of input arguments were implicitly ignored. .. _splin: splin.html .. _interpln: interpln.html .. _interp: interp.html