Error useing axis set

Hello. I needed to make a program for university in witch to i needed to code the finite elementh method useing triangles. I wanted to make the figure in witch i was showing the triangles a bit more visible so i used an axis to make it a bit wider but i get the following error: Error using set Bad property value found. Object Name : axes Property Name : 'YLim' Values must be increasing and non-NaN.

Error in axis>LocSetLimits (line 208) set(ax,...

Error in axis (line 94) LocSetLimits(ax(j),cur_arg);

Error in Metoda_elementului_finit_cu_dreptunghiuri (line 63) axis([a-0.2,b+0.2,c-0.2,d+0.2])

The program is as fallowing:

if true
  % function []=Metoda_elementului_finit_cu_dreptunghiuri()
end
a=input('a=');
b=input('b=');
d=input('c=');
c=input('d=');
N=input('N=');
M=input('M=');
Nod=zeros((N+1)*(M+1),3);
Dr=zeros(N*M,4);
x=linspace(a,b,N+1);
y=linspace(c,d,M+1);
k1=0;
for j=1:M+1
 for i=1:N+1 
     k=i+(N+1)*(j-1);
     Nod(k,1)=x(i);
      Nod(k,2)=y(j);
      Nod(k,3)=0;
      if((i~=1)&&(i~=N+1)&&(j~=1)&&(j~=M+1))
          k1=k1+1;
          Nod(k,3)=k1;
      end
 end

 end
display(Nod);
%afisarea
figure(1)
%linii verticale
for i=1:N+1
    plot(x(i)*ones(1,M+1),y)
    hold on
    %pause(0.2)
end
%linii orizontale
for j=1:M+1
    plot(x,y(j)*ones(1,N+1))
    hold on
    %pause(0.2)
end
for k=1:(N+1)*(M+1)
    if Nod(k,3)==0
        plot (Nod(k,1),Nod(k,2),'*b')
        hold on
    else
        plot(Nod(k,1),Nod(k,2),'or')
    hold on
    end
    axis([a-0.2,b+0.2,c-0.2,d+0.2])
 end

 %matricea dreptunghiurilor
kT=0;
for j=1:M+1
    for i=1:N+1
        k=i+(N+1)*(j-1);
        if(i<=N)&&(j<=M)
            kT=kT+1;
            Dr(kT,1)=k;
            Dr(kT,2)=k+N+1;
            Dr(kT,3)=k+N+2;
            Dr(kT,4)=k+1;           
        end
    end
 end
display(Dr);

 MR=zeros((N-1)*(M-1));
L=zeros((N-1)*(M-1),1);
nd=N*M;
for k=1:nd
    xd=zeros(4,1);
    yd=zeros(4,1);
    for j=1:4
        xd(j)=Nod(Dr(k,j),1);
        yd(j)=Nod(Dr(k,j),2);
    end
D=zeros(4);
for j=1:4
    D(1:4,j)=[xd(j)*yd(j);xd(j);yd(j);1];
end
Dinv=inv(D);
A=Dinv(1:4,1);
B=Dinv(1:4,2);
C=Dinv(1:4,3);
Me=zeros(4);
Le=zeros(4,1);
aDr=(xd(3)- xd(1))*(yd(2)-yd(1));
for i=1:4
    for j=1:4
        R=((A(i)*A(j)*(yd(2)^2 + yd(1)*yd(2) +...
            yd(1)^2 + xd(3)^2 + xd(3)*xd(1) + ...
            xd(1)^2 )*1/3)+(A(i)*B(j)+A(j)*B(i))...
            *(y(2)+y(1))+(A(i)*C(j)+A(j)*C(i))*(x(3)+...
            x(1))*1/2 +B(i)*B(j)+C(i)*C(j))*aDr;
        Me(i,j)=R;
    end
    Le(i)=(f(xd(i),yd(i))*aDr/4);
end
display(Me)
display(Le)
for i=1:4
    for j=1:4
        if((Nod(Dr(k,i),3)~=0) && (Nod(Dr(k,j),3)~=0))
            MR(Nod(Dr(k,i),3),(Nod(Dr(k,j),3)))=...
                MR(Nod(Dr(k,i),3),(Nod(Dr(k,j),3)))+Me(i,j);
        end
        if(Nod(Dr(k,i),3)~=0)
            L(Nod(Dr(k,i),3))=L(Nod(Dr(k,i),3))+Le(i);
        end
    end
end
end
display(MR);
display(L);

 function[z]=f(x,y)
z=2.*sin(x).*sin(y);
end

end

Thanks in advance!

Answer 1

[Star Strider]

My guess is that the error is in this axis call, since I don’t see any others:

axis([a-0.2,b+0.2,c-0.2,d+0.2])

If you only want to make the axis limits larger, this will probably work:

axlims = [get(gca, 'XLim')  get(gca, 'YLim')];
axis(axlims + [-0.2  0.2  -0.2  0.2])

Put those two lines in place of your current axis call. That should solve your problem.

[Milu Mihai]

Thanks alot.It works but considering the values i give are small the figure it's very small and you can't really see anything(the points that are supposed to be seen),unless i zoom in. For example for a=0,b=pi,c=0,d=pi,N=10,M=10 the figure will be a 27.7X27.7 square instead of something like (pi+0.2)X(pi+0.2) Is there any way to close the gap?

[Star Strider]

My pleasure.

One option is to multiply them by the adjustment vector instead of adding them:

axis(sign(axlims) .* (abs(axlims) .* [1+0.2,  1+0.2,  1+0.2,  1+0.2]))

This works correctly for both positive and negative axis limits. Adjust the offset values (here all 0.2) to get the result you want.