Check out the first example:
help interp1
INTERP1 1-D interpolation (table lookup)
Vq = INTERP1(X,V,Xq) interpolates to find Vq, the values of the
underlying function V=F(X) at the query points Xq.
X must be a vector. The length of X is equal to N.
If V is a vector, V must have length N, and Vq is the same size as Xq.
If V is an array of size [N,D1,D2,...,Dk], then the interpolation is
performed for each D1-by-D2-by-...-Dk value in V(i,:,:,...,:). If Xq
is a vector of length M, then Vq has size [M,D1,D2,...,Dk]. If Xq is
an array of size [M1,M2,...,Mj], then Vq is of size
[M1,M2,...,Mj,D1,D2,...,Dk].
Vq = INTERP1(V,Xq) assumes X = 1:N, where N is LENGTH(V)
for vector V or SIZE(V,1) for array V.
Interpolation is the same operation as "table lookup". Described in
"table lookup" terms, the "table" is [X,V] and INTERP1 "looks-up"
the elements of Xq in X, and, based upon their location, returns
values Vq interpolated within the elements of V.
Vq = INTERP1(X,V,Xq,METHOD) specifies the interpolation method.
The available methods are:
'linear' - (default) linear interpolation
'nearest' - nearest neighbor interpolation
'next' - next neighbor interpolation
'previous' - previous neighbor interpolation
'spline' - piecewise cubic spline interpolation (SPLINE)
'pchip' - shape-preserving piecewise cubic interpolation
'cubic' - cubic convolution interpolation for uniformly-spaced
data. This method does not extrapolate and falls back to
'spline' interpolation for irregularly-spaced data.
NOTE: 'cubic' changed in R2020b to perform cubic convolution.
In previous releases, 'cubic' was the same as 'pchip'.
'v5cubic' - same as 'cubic'
'makima' - modified Akima cubic interpolation
Vq = INTERP1(X,V,Xq,METHOD,'extrap') uses the interpolation algorithm
specified by METHOD to perform extrapolation for elements of Xq outside
the interval spanned by X.
Vq = INTERP1(X,V,Xq,METHOD,EXTRAPVAL) replaces the values outside of
the interval spanned by X with EXTRAPVAL. NaN and 0 are often used for
EXTRAPVAL. The default extrapolation behavior with four input
arguments is 'extrap' for 'spline', 'pchip' and 'makima', and
EXTRAPVAL = NaN (NaN+NaN*1i for complex values) for the other methods.
PP = INTERP1(X,V,METHOD,'pp') is not recommended. Use
griddedInterpolant instead.
PP = INTERP1(X,V,METHOD,'pp') uses the interpolation algorithm
specified by METHOD to generate the ppform (piecewise polynomial form)
of V. The method may be any of the above METHOD except for 'v5cubic'
and 'makima'. PP may then be evaluated via PPVAL. PPVAL(PP,Xq) is the
same as INTERP1(X,V,Xq,METHOD,'extrap').
For example, generate a coarse sine curve and interpolate over a
finer abscissa:
X = 0:10; V = sin(X); Xq = 0:.25:10;
Vq = interp1(X,V,Xq); plot(X,V,'o',Xq,Vq,':.')
For a multi-dimensional example, we construct a table of functional
values:
X = [1:10]'; V = [ X.^2, X.^3, X.^4 ];
Xq = [ 1.5, 1.75; 7.5, 7.75]; Vq = interp1(X,V,Xq);
creates 2-by-2 matrices of interpolated function values, one matrix for
each of the 3 functions. Vq will be of size 2-by-2-by-3.
Class support for inputs X, V, Xq, EXTRAPVAL:
float: double, single
See also INTERPFT, SPLINE, PCHIP, INTERP2, INTERP3, INTERPN, PPVAL,
griddedInterpolant, scatteredInterpolant.
Documentation for interp1
doc interp1
Other uses of interp1
codistributed/interp1 dlarray/interp1 gpuArray/interp1
datetime/interp1 duration/interp1
