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Please note that the recommended version of Scilab is 2025.0.0. This page might be outdated.
See the recommended documentation of this function
detrend
remove constant, linear or piecewise linear trend from a vector
Calling Sequence
y = detrend(x) y = detrend(x,flag) y = detrend(x,flag,bp)
Arguments
- x
vector or matrix of real or complex numbers (the signal to treat)
- flag
a string equal to "linear" (or "l") for linear or piecewise linear treatment or "constant" (or "c") for constant treatment.
- bp
the breakpoints to provide if you want a piecewise linear treatment.
- y
output, the signal x with the trend removed from it.
Description
This function removes the constant or linear or
piecewise linear trend from a vector x
. In general
this can be useful before a fourier analysis. If x
is
matrix this function removes the trend of each column of x.
When flag
= "constant" or "c" detrend
removes the constant trend
(simply the mean of the signal) and when flag
= "linear" or "l" the function
removes the linear trend. By adding a third argument bp
it is possible to
remove a continuous piecewise linear trend. Note that the "instants" of the signal
x
goes from 0 to m-1 (m = length(x) if x is a vector and m = size(x,1) in case
x is a matrix). So the breakpoints bp(i)
must be reals in [0 m-1]
(breakpoints outside are simply removed from bp
vector).
The trend is got by a least square fit of x
on the appropriate function space.
Examples
// example #1 t = linspace(0,16*%pi,1000)'; x = -20 + t + 0.3*sin(0.5*t) + sin(t) + 2*sin(2*t) + 0.5*sin(3*t); y = detrend(x); clf() plot2d(t,[x y],style=[2 5]) legend(["before detrend","after detrend"]); xgrid() // example #2 t = linspace(0,32*%pi,2000)'; x = abs(t-16*%pi) + 0.3*sin(0.5*t) + sin(t) + 2*sin(2*t) + 0.5*sin(3*t); y = detrend(x,"linear",1000); clf() plot2d(t,[x y],style=[2 5]) legend(["before detrend","after detrend"]); xgrid()
Authors
Bruno Pincon
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