Parameters estimation on Lotka Volterra model with Scilab -


i'm trying make parameters estimation on lotka-volterra model scilab (i total neophyte). when try run script, scilab warns incoherent subtraction. guess problem same in this topic, solution there uses matlab function.

here script:

// 1. create lotka volterra function  function [dy]=lotkavolterra(t,x,c,n,m,e)     ingestc = c * x(1) * x(2)     growthp = n * x(1)     mortc = m * x(2)     dy(1) = growthp - ingestc     dy(2) = ingestc * e - mortc endfunction  // 2. define nonlinear least squares functions  function f = differences ( x )      // returns difference between simulated differential      // equation , experimental data.     c = x(1) ;n = x(2);m = x(3);e = x(4);y0 = y_exp(1,:);t0 = 0     y_calc=ode(y0',t0,t,list(lotkavolterra,c,n,m,e))      diffmat = y_calc' - y_exp     f = diffmat(:) endfunction   function val = l_squares ( x )      // computes sum of squares of differences.     f = differences ( x )      val = sum(f.^2) endfunction   // experimental data  t = [0:19]';  h=[20,20,20,12,28,58,75,75,88,61,75,88,69,32,13,21,30,2,153,148]; l=[30,45,49,40,21,8,6,5,10,20,33,34,30,21,14,8,4,4,14,38]; y_exp=[h',l'];   // compute model cost function function [f, g, ind] = modelcost (x, ind)     f = l_squares ( x )     g = derivative ( l_squares , x ) endfunction  // use of optim function loops avoid local minimum  tic i=0 fitminx=zeros(4,100); fitminy=zeros(1,100); c=[0:0.1:1]     n=[0:0.1:1]         m=[0:0.1:1]             e=[0:0.1:1]                 i=i+1                 x0 = [c;n;m;e]                 [ fopt , xopt , gopt ] = optim ( modelcost , x0 )                 fitminx(:,i)=xopt;                 fitminy(:,i)=fopt;             end         end     end  end [a,b]=min(fitminy) fitminx(:,a) toc

the error message :

lsoda--  @ t (=r1), mxstep (=i1) steps    needed before reaching tout       i1 :        500                                                         r1 :   0.4145715729197d+01                                        attention : le résultat est peut être inexact.   !--error 9  soustraction incohérente. @ line       4 of function differences called :   @ line       2 of function l_squares called :   @ line      16 of function %r_ called :   @ line      15 of function %deriv1_ called :   @ line      58 of function derivative called :   @ line       3 of function modelcost called :                   [ fopt , xopt , gopt ] = optim ( modelcost , x0 )

thanks interest , time give problem (and sorry english)

duplicate of answer here

the problem solver somehow reach point cannot solve ode on every t , stops @ point. y_calc smaller y_exp in size.

if not problem you, solved changing diffmat on line 6 of differences function 

diffmat = y_calc' - y_exp(1:size(y_calc',1),:)

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