MATLAB: Undefined function or variable ‘x’. Where the error are

undefined function or variable 'x'.

Hi,
The matlab point this error: Error in crime_back_forw11_12 (line 93) n22 = -m-beta*((lambda1(j)-h2*n11)-(lambda2(j)-h2*n12))-alpha*(0.5*(x1(j)+x1(j-1)))*(u1(j))*((lambda1(j)-h2*n11)-(lambda2(j)-h2*n12))+alpha*(0.5*(x1(j)+x(j-1)))*((lambda1(j)-h2*n11)-(lambda2(j)-h2*n12))+(u2(j))*gama*(lambda2(j)-h2*n12-lambda3(j)-h2*n13); Undefined function or variable 'x' >> My algorithm is: function y = crime_back_forw11_12
test = -1;
tf= 3; mu = 0.001; M = 999; t = linspace(0,1,M+1); h = 1/M; h2 = h/2;
beta=0.1; alpha=0.7; gama=0.03; delta=0.7; epsilon=0.3; m=100; n=100; p=50; d=25;
x1= zeros(1,M+1); x2= zeros(1,M+1); x3= zeros(1,M+1);
u1= zeros(1,M+1); u2= zeros(1,M+1); u3= zeros(1,M+1);
lambda1 = zeros(1,M+1); lambda2 = zeros(1,M+1); lambda3 = zeros(1,M+1);
x1(1) = 0.0555; x2(1) = 0.0003; x3(1) = 0.0004;
while(test < 0)
    oldu1 = u1;
    oldu2 = u2;
    oldu3 = u3;
    oldx1 = x1;
    oldx2 = x2;
    oldx3 = x3;
    oldlambda1 = lambda1;
    oldlambda2 = lambda2;
    oldlambda3 = lambda3;    
    for i = 1:M
        m11 = beta*x2(i)-alpha*x1(i)*x2(i)*(1-u1(i))+u3(i)*epsilon*x3(i);
        m12 = -beta*x2(i)+alpha*x1(i)*x2(i)*(1-u1(i))-u2(i)*gama*x2(i)+(1-u3(i))*delta*x3(i);
        m13 = u2(i)*gama*x2(i)-(1-u3(i))*delta*x3(i)-u3(i)*epsilon*x3(i);        
        m21 = beta*(x2(i)+h2*m12)-alpha*(x1(i)+h2*m11)*(x2(i)+h2*m12)*(1-0.5*(u1(i)+u1(i+1)))+0.5*(u3(i)+u3(i+1))*epsilon*(x3(i)+h2*m13);
        m22 = -beta*(x2(i)+h2*m12)+alpha*(x1(i)+h2*m11)*(x2(i)+h2*m12)*(1-0.5*(u1(i)-u1(i+1))-0.5*(u2(i)-u2(i+1))*gama*(x2(i)+h2*m12)+(1-0.5*(u3(i)-u3(i+1)))*delta*(x3(i)+h2*m13));
        m23 = 0.5*(u2(i)-u2(i+1))*gama*(x2(i)+h2*m12)-(1-0.5*(u3(i)+u3(i+1))*delta*(x3(i)+h2*m13)-(u3(i)+u3(i+1))*epsilon*(x3(i)+h2*m13));
        m31 = beta*(x2(i)+h2*m22)-alpha*(x1(i)+h2*m21)*(x2(i)+h2*m22)*(1-0.5*(u1(i)+u1(i+1)))+0.5*(u3(i)+u3(i+1))*epsilon*(x3(i)+h2*m23);
        m32 = -beta*(x2(i)+h2*m22)+alpha*(x1(i)+h2*m21)*(x2(i)+h2*m22)*(1-0.5*(u1(i)-u1(i+1))-0.5*(u2(i)-u2(i+1))*gama*(x2(i)+h2*m22)+(1-0.5*(u3(i)-u3(i+1)))*delta*(x3(i)+h2*m23));
        m33 = 0.5*(u2(i)-u2(i+1))*gama*(x2(i)+h2*m22)-(1-0.5*(u3(i)+u3(i+1))*delta*(x3(i)+h2*m23)-(u3(i)+u3(i+1))*epsilon*(x3(i)+h2*m23));
        m41 = beta*(x2(i)+h2*m32)-alpha*(x1(i)+h2*m31)*(x2(i)+h2*m32)*(1-u1(i+1))+u3(i+1)*epsilon*(x3(i)+h2*m33);
        m42 = -beta*(x2(i)+h2*m32)+alpha*(x1(i)+h2*m31)*(x2(i)+h2*m32)*(1-u1(i+1))-u2(i+1)*gama*(x2(i)+h2*m32)+(1- u3(i+1))*delta*(x3(i)+h2*m33);
        m43 = u2(i+1)*gama*(x2(i)+h2*m32)-(1-(u3(i+1)))*delta*(x3(i)+h2*m33)-u3(i+1)*epsilon*(x3(i)+h2*m33);
        x1(i+1) = x1(i) + (h/6)*(m11 + 2*m21 + 2*m31 + m41);
        x2(i+1) = x2(i) + (h/6)*(m12 + 2*m22 + 2*m32 + m42);
        x3(i+1) = x3(i) + (h/6)*(m13 + 2*m23 + 2*m33 + m43);
    end
    for i = 1:M
        j = M + 2 - i;
        n11 = alpha*x2(j)*(1-u1(j))*(lambda1(j)-lambda2(j));
        n12 = -m-beta*(lambda1(j)-lambda2(j))-alpha*x1(j)*u1(j)*(lambda1(j)-lambda2(j))+alpha*x1(j)*(lambda1(j)-lambda2(j))+gama*u2(j)*(lambda2(j)-lambda3(j));
        n13 = u3(j)*epsilon*(lambda3(j)-lambda1(j))+(1-u3(j))*delta*(-lambda2(j)+lambda3(j));
        n21 = alpha*(0.5*(x2(j)+x2(j-1)))*(1-u1(j))*((lambda1(j)-h2*n11)-(lambda2(j)-h2*n11));
        n22 = -m-beta*((lambda1(j)-h2*n11)-(lambda2(j)-h2*n12))-alpha*(0.5*(x1(j)+x1(j-1)))*(u1(j))*((lambda1(j)-h2*n11)-(lambda2(j)-h2*n12))+alpha*(0.5*(x1(j)+x(j-1)))*((lambda1(j)-h2*n11)-(lambda2(j)-h2*n12))+(u2(j))*gama*(lambda2(j)-h2*n12-lambda3(j)-h2*n13);
        n23 = u3(j)*epsilon*((lambda3(j)-h2*n13)-(lambda1(j)-h2*n11))+(1-(u3(j)))*delta*((-lambda2(j)-h2*n12)+(lambda3(j)-h2*n13));       
        n31 = alpha*0.5*(x2(j)+x2(j-1))*(1-u1(j))*((lambda1(j)-h2*n21)-(lambda2(j)-h2*n21));
        n32 = -m-beta*((lambda1(j)-h2*n21)-(lambda2(j)-h2*n22))-alpha*0.5*(x1(j)+x1(j-1))*(u1(j))*((lambda1(j)-h2*n21)-(lambda2(j)-h2*n22))+alpha*0.5*(x1(j)+x(j-1))*((lambda1(j)-h2*n21)-(lambda2(j)-h2*n22))+(u2(j))*gama*(lambda2(j)-h2*n22-lambda3(j)-h2*n23);
        n33 = u3(j)*epsilon*((lambda3(j)-h2*n23)-(lambda1(j)-h2*n21))+(1-(u3(j)))*delta*((-lambda2(j)-h2*n22)+(lambda3(j)-h2*n23));        
        n41 = alpha*(x2(j-1))*(1-u1(j))*((lambda1(j)-h2*n31)-(lambda2(j)-h2*n31));
        n42 = -m-beta*((lambda1(j)-h2*n31)-(lambda2(j)-h2*n32))-alpha*(x1(j-1))*(u1(j))*((lambda1(j)-h2*n31)-(lambda2(j)-h2*n32))+alpha*(x1(j-1))*((lambda1(j)-h2*n31)-(lambda2(j)-h2*n32))+(u2(j))*gama*(lambda2(j)-h2*n32-lambda3(j)-h2*n33);
        n43 = u3(j)*epsilon*((lambda3(j)-h2*n33)-(lambda1(j)-h2*n31))+(1-(u3(j)))*delta*((-lambda2(j)-h2*n32)+(lambda3(j)-h2*n33));        
        lambda1(j-1) = lambda1(j) - h/6*(n11 + 2*n21 + 2*n31 + n41);
        lambda2(j-1) = lambda2(j) - h/6*(n12 + 2*n22 + 2*n32 + n42);
        lambda3(j-1) = lambda3(j) - h/6*(n13 + 2*n23 + 2*n33 + n43);

Best Answer

Here:
n22 = -m-beta*((lambda1(j)-h2*n11)-(lambda2(j)-h2*n12))-alpha*(0.5*(x1(j)+x1(j-1)))*(u1(j))*((lambda1(j)-h2*n11)-(lambda2(j)-h2*n12))+alpha*(0.5*(x1(j)+x(j-1)))*((lambda1(j)-h2*n11)-(lambda2(j)-h2*n12))+(u2(j))*gama*(lambda2(j)-h2*n12-lambda3(j)-h2*n13); 
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It needs to be ‘x1’, or ‘x2’ or one of the others.
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