This function will approximate the first derivative 
(gradient) of a function
at the actual time 
with respect to the values of the last three function calls according to the BDF method:
|
xEnable |
BOOL |
reset (see CAA Guidelines) |
|
lrInputValue |
LREAL |
actual function value |
|
udiTM |
UDINT |
length of time interval |
|
lrDerivative |
LREAL |
approximated value of first derivative |
|
xValid |
BOOL |
validity of result; will be set to FALSE, if the number of calls necessary for approximating has not been executed yet |
(equals time passed since last call to function)