getting an error: ''unable to resolve the name handles.edit_t"

% General Parameters
t=str2double(get(handles.edit_t,'string'));
lattice=str2double(get(handles.edit_lattice,'String'));

%starting with 3D representation

% creating the necessary k-vectors for the calculation
k_x= linspace(-2*pi/(lattice), 2*pi/(lattice), 100);
k_y= linspace(-2*pi/(lattice), 2*pi/(lattice), 100);
[k_meshx,k_meshy]= meshgrid(k_x, k_y);

%Energy values with the preset parameters in 3D representation
energy_mesh=NaN([size(k_meshx,1), size(k_meshx,2),2]);
b1=2.13;
b2=1.138;
for a=1:size(k_meshx,1)
    energy_mesh(:,a,1)=t*sqrt(3+2*cos(2*b1*k_meshy)+4*cos(b2*k_meshx)*cos(b1*k_meshy));
    energy_mesh(:,a,2)=-t*sqrt(3+2*cos(2*b1*k_meshy)+4*cos(b2*k_meshx)*cos(b1*k_meshy));
end

% Graphic representation
set(handles.axes_mesh,'color','w')
set(handles.axes_mesh,'NextPlot','replace')
surf(k_meshx,k_meshy,real(energy_mesh(:,:,1)),'parent', handles.axes_mesh,'FaceAlpha',0.6)
set(handles.axes_mesh,'NextPlot','add')
hold on
surf(k_meshx,k_meshy,real(energy_mesh(:,:,2)),'parent', handles.axes_mesh,'FaceAlpha',0.6)
colormap('jet')
shading interp

% plot of brillouin zone (black) and triangular path (red) of the dispersion plot
plot3(2*pi/(sqrt(3)*lattice)*[1,0,-1,-1,0,1,1], 2*pi/(3*lattice)*[1,2,1,-1,-2,-1,1],'k-','Linewidth',2,'parent',handles.axes_mesh)
plot3(2*pi/(lattice*sqrt(3))*[0,1,1,0], 2*pi/(3*lattice)*[0,0,1,0],'r-','Linewidth',2,'parent',handles.axes_mesh)
hx=xlabel('k_x','parent', handles.axes_mesh);
hy=ylabel('k_y','parent', handles.axes_mesh);
hz=zlabel('E(k)','parent', handles.axes_mesh);
axis equal
grid off
hold off

[Jan]

The shown code fails in the 1st line already. Then the rest of the code is not useful to identify the problem.

What is handles in your code?