Sorry the ode call should be (y0 first, then x0)
y = ode(-1,x0,x1,list(f,x1,y1,d1))
The elapsed time seems OK:
--> tic;y = ode(-1,x0,x1,list(f,x1,y1,d1));toc
ans =
0.002235
S.
Le 11/02/2020 à 08:17, Stéphane Mottelet a écrit :
Hello,
The usual way to compute a primitive would be to use ode, like this:
function out=f(x, y, x1, y1, d1)
out = interp(x,x1,y1,d1)
endfunction
x0 = 0
x1 = 0:0.01:2*%pi;
y1 = sin(x1);
d1 = splin(x1,y1);
y = ode(x0,-1,x1,list(f,x1,y1,d1))
Your proposition is very slow because you are recomputing the spline
many times.
S.
Le 10/02/2020 à 20:52, Federico Miyara a écrit :
Dear all,
The function integrate() is very handy to obtain a numerical primtive
of a function, particularly useful when there is no closed form for
the primitive or it is too involved. According to the documentation
x = integrate(expr, v, x0, x1 [, atol [, rtol]])
expr: a character string defining a Scilab expression.
v: a character string, the integration variable name
However there is a case that would be interesting to handle, and it
is when one has a set of experimental (or simulated) data xk, yk.
Here there is no expression defining a function.
One way to circumvent this is using as the expression some sort of
interpolator such as
x = integrate("interp1(xk, yk, x, ''spline'')", "x", x0, x1)
This works, but for some reason I don't quite understand it is very slow.
For instance,
x0 = 0
x1 = 0:0.01:2*%pi;
y1 = sin(x1);
tic
X = integrate("interp1(x1, y1, x, ''spline'')", "x", x0, x1);
toc
Requires 27 s to execute. In the meantime, control is seemingly
returned to the console, one can enter instructions, but then the
program freezes until the integrate comand finishes.
Changing "spline" to "linear" even worsens it rising to 33 s.
Has anybody an idea of what can be happening?
Maybe it computes the full interpolator for each single point? Even
if so, I have only 629 values of the independent variable.
Regards,
Federico Miyara
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--
Stéphane Mottelet
Ingénieur de recherche
EA 4297 Transformations Intégrées de la Matière Renouvelable
Département Génie des Procédés Industriels
Sorbonne Universités - Université de Technologie de Compiègne
CS 60319, 60203 Compiègne cedex
Tel : +33(0)344234688
http://www.utc.fr/~mottelet
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--
Stéphane Mottelet
Ingénieur de recherche
EA 4297 Transformations Intégrées de la Matière Renouvelable
Département Génie des Procédés Industriels
Sorbonne Universités - Université de Technologie de Compiègne
CS 60319, 60203 Compiègne cedex
Tel : +33(0)344234688
http://www.utc.fr/~mottelet
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