From 7dfcc480ba1e19bd3232349fc733caef94034292 Mon Sep 17 00:00:00 2001
From: stainer_t <thomas.stainer@oecd-nea.org>
Date: Mon, 8 Sep 2025 13:48:49 +0200
Subject: Initial commit from Polytechnique Montreal

---
 Donjon/src/DETFIL.f | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 Donjon/src/DETFIL.f

(limited to 'Donjon/src/DETFIL.f')

diff --git a/Donjon/src/DETFIL.f b/Donjon/src/DETFIL.f
new file mode 100644
index 0000000..cb4b16c
--- /dev/null
+++ b/Donjon/src/DETFIL.f
@@ -0,0 +1,45 @@
+*DECK DETFIL
+      SUBROUTINE DETFIL(Y,X,XL,TC,DT,N)
+*
+*----------------------------------------------------------------------
+*
+*Purpose:
+* Filters the n values of x vector for TC seconds.
+* Formulations are taken from the expression of the different
+* equation of a filter with a linear variation of x in DT time
+* step.
+*
+*Author(s): 
+* xxx
+*
+*Parameters:
+* Y   real variables Y(I) at previous time
+* X   real variables to filtered
+* XL  real variables X(I) at previous time
+* TC  filter time constant
+* DT  time step between two calculations
+* N   dimension of the vectors X,XL,Y
+*
+*--------------------------------------------------------------------
+*
+      IMPLICIT NONE
+      INTEGER  N,I
+      REAL     Y(N),X(N),XL(N),TC,DT,AA,A,B,C
+*
+*     COMPUTE PONDERATION FACTORS FOR Y,X ET XL
+*
+      AA =  - DT / TC
+      A  = EXP ( AA )
+      B  = 1. - A
+      C  = 1. - B * TC/DT
+*
+*     COMPUTE NEW Y
+*
+      DO 10 I=1,N
+*
+        Y(I)  = A * Y(I) + ( B - C ) * XL(I) + C * X(I)
+        XL(I) = X(I)
+*
+ 10   CONTINUE
+      RETURN
+      END
-- 
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