Thread Subject:

algebraic loop error

when using Ipold= Ip in this embedded function code

function [e,Pm,Ip] = new(In,Vn)
persistent Ipold ;
if isempty(Ipold)
   Ipold=2; %initialized only once in the beginning
end
K1=2;
K2=-.195;
Pn= Vn*In
Pm=100*In
e= Pn-Pm
if Pn>Pm
Ip = Ipold+K1 *e
end
Ip = Ipold+K2 *e
Ipold=Ip



error message appeared
"Trouble solving algebraic loop containing 'chee_pv/pv6/Algebraic Constraint/Initial Guess' at time 0. Stopping simulation. There may be a singularity in the solution. If the model is correct, try reducing the step size (either by reducing the fixed step size or by tightening the error tolerances)"

"mado " <elec_mnf@yahoo.com> wrote in message <k9ard0$l76$1@newscl01ah.mathworks.com>...
> if Pn>Pm
> Ip = Ipold+K1 *e
> end
> Ip = Ipold+K2 *e
- - - - - - - - - -
  There is something amiss in your code. The 'if-end' result is totally ignored:

 if Pn>Pm
  Ip = Ipold+K1 *e
 end
 Ip = Ipold+K2 *e

Regardless of whether Pn is greater than Pm or not, the result is always the same. The line "Ip = Ipold+K2*e" overwrites whatever change was made to 'Ip' in the 'if' construct. I am sure you meant something else.

Roger Stafford

.

error message came even if i correct the if condition to

 if Pn>Pm
  Ip = Ipold+K1 *e
else
Ip = Ipold+K2 *e
 end
but this time with this line Ipold =Ip or without .

"mado " <elec_mnf@yahoo.com> wrote in message <k9bbgj$er1$1@newscl01ah.mathworks.com>...
> .
>
> error message came even if i correct the if condition to
>
> if Pn>Pm
> Ip = Ipold+K1 *e
> else
> Ip = Ipold+K2 *e
> end
> but this time with this line Ipold =Ip or without .

any suggestion please??

"mado " <elec_mnf@yahoo.com> wrote in message <k9ard0$l76$1@newscl01ah.mathworks.com>...
> "Trouble solving algebraic loop containing 'chee_pv/pv6/Algebraic Constraint/Initial Guess' at time 0. Stopping simulation. There may be a singularity in the solution. If the model is correct, try reducing the step size (either by reducing the fixed step size or by tightening the error tolerances)"
- - - - - - - - -
  It looks as though this error message is associated with the way you are using 'new' rather than being about 'new' itself. Are you using Simulink? If I were you, I would read that message very carefully and see if it contains a clue as what the trouble is. It seems to hint that some iteration you have set up, presumably involving 'new', is not converging properly.

Roger Stafford

what is "new" do you mean ???
yes its simulink, and this code is included in embedded matlab function