Simple tests showing how to use external functions.

tests/external_function/example1_1st_and_2nd_deriv_functions_provided.mod

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+// Example 1 from Collard's guide to Dynare
+var y, c, k, a, h, b;
+varexo e, u;
+
+parameters beta, rho, alpha, delta, theta, psi, tau;
+
+alpha = 0.36;
+rho   = 0.95;
+tau   = 0.025;
+beta  = 0.99;
+delta = 0.025;
+psi   = 0;
+theta = 2.95;
+
+phi   = 0.1;
+
+external_function(nargs=2, name=extFunWithFirstAndSecondDerivs, first_deriv_provided, second_deriv_provided);
+
+model;
+c*theta*h^(1+psi)=(1-alpha)*y;
+k = beta*(((exp(b)*c)/(exp(b(+1))*c(+1)))
+    *(exp(b(+1))*alpha*y(+1)+(1-delta)*k));
+y = exp(a)*(k(-1)^alpha)*(h^(1-alpha));
+k = exp(b)*(y-c)+extFunWithFirstAndSecondDerivs((1-delta),k(-1));
+a = rho*a(-1)+tau*b(-1) + e;
+b = tau*a(-1)+rho*b(-1) + u;
+end;
+
+initval;
+y = 1.08068253095672;
+c = 0.80359242014163;
+h = 0.29175631001732;
+k = 11.08360443260358;
+a = 0;
+b = 0;
+e = 0;
+u = 0;
+end;
+
+shocks;
+var e; stderr 0.009;
+var u; stderr 0.009;
+var e, u = phi*0.009*0.009;
+end;
+
+stoch_simul;

tests/external_function/example1_1st_deriv_function_provided.mod

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+// Example 1 from Collard's guide to Dynare
+var y, c, k, a, h, b;
+varexo e, u;
+
+parameters beta, rho, alpha, delta, theta, psi, tau;
+
+alpha = 0.36;
+rho   = 0.95;
+tau   = 0.025;
+beta  = 0.99;
+delta = 0.025;
+psi   = 0;
+theta = 2.95;
+
+phi   = 0.1;
+
+external_function(nargs=2, name=extFunNoDerivs, first_deriv_provided=extFunDeriv);
+
+model;
+c*theta*h^(1+psi)=(1-alpha)*y;
+k = beta*(((exp(b)*c)/(exp(b(+1))*c(+1)))
+    *(exp(b(+1))*alpha*y(+1)+(1-delta)*k));
+y = exp(a)*(k(-1)^alpha)*(h^(1-alpha));
+k = exp(b)*(y-c)+extFunNoDerivs((1-delta),k(-1));
+a = rho*a(-1)+tau*b(-1) + e;
+b = tau*a(-1)+rho*b(-1) + u;
+end;
+
+initval;
+y = 1.08068253095672;
+c = 0.80359242014163;
+h = 0.29175631001732;
+k = 11.08360443260358;
+a = 0;
+b = 0;
+e = 0;
+u = 0;
+end;
+
+shocks;
+var e; stderr 0.009;
+var u; stderr 0.009;
+var e, u = phi*0.009*0.009;
+end;
+
+stoch_simul;

tests/external_function/example1_no_deriv_functions_provided.mod

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+// Example 1 from Collard's guide to Dynare
+var y, c, k, a, h, b;
+varexo e, u;
+
+parameters beta, rho, alpha, delta, theta, psi, tau;
+
+alpha = 0.36;
+rho   = 0.95;
+tau   = 0.025;
+beta  = 0.99;
+delta = 0.025;
+psi   = 0;
+theta = 2.95;
+
+phi   = 0.1;
+
+model;
+c*theta*h^(1+psi)=(1-alpha)*y;
+k = beta*(((exp(b)*c)/(exp(b(+1))*c(+1)))
+    *(exp(b(+1))*alpha*y(+1)+(1-delta)*k));
+y = exp(a)*(k(-1)^alpha)*(h^(1-alpha));
+k = exp(b)*(y-c)+extFunNoDerivs((1-delta),k(-1));
+a = rho*a(-1)+tau*b(-1) + e;
+b = tau*a(-1)+rho*b(-1) + u;
+end;
+
+initval;
+y = 1.08068253095672;
+c = 0.80359242014163;
+h = 0.29175631001732;
+k = 11.08360443260358;
+a = 0;
+b = 0;
+e = 0;
+u = 0;
+end;
+
+shocks;
+var e; stderr 0.009;
+var u; stderr 0.009;
+var e, u = phi*0.009*0.009;
+end;
+
+stoch_simul;

tests/external_function/extFunDeriv.m

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+function df=extFunDeriv(a,b)
+da=b^2;
+db=2*a*b;
+df=[da db];
+end

tests/external_function/extFunNoDerivs.m

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+function y=extFunNoDerivs(a,b)
+y=a*(b^2);
+end

tests/external_function/extFunWithFirstAndSecondDerivs.m

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+function [y df d2f]=extFunWithFirstAndSecondDerivs(a,b)
+y=a*(b^2);
+
+da=b^2;
+db=2*a*b;
+df=[da db];
+
+d2f=[0 2*b; 2*b 2*a];
+end