the plot is not appearing what should i fix ?

 g=9.81;
            Flow = app.FlowEditField.Value;
            Width = app.WidthEditField.Value;
            q = Width/Flow;
            yc=(q^2/g)^(1/3);
            Criticaldepth = app.CriticalDepthEditField.Value; 
            app.CriticalDepthEditField.Value = [num2str(yc)];
            Depth = app.DepthEditField.Value;
 for i=1:length(Depth)
     E(i)=Depth(i)+q^2/(2*g*Depth(i)^2);
            plot(app.UIAxes,E,Depth,'r');
 end

Answer 1

[Walter Roberson]

 for i=1:length(Depth)
     E(i)=Depth(i)+q^2/(2*g*Depth(i)^2);
 end
 plot(app.UIAxes,E,Depth,'r');

However, the convention is that the independent variable (Depth in this case) should be on the horizontal axes (first data parameter) and that the dependent variable (E in this case) should be on the vertical axes. It will be confusing to people that you have those reversed.

Note: instead of the loop you could vectorize to

 E = Depth + q^2 ./ (2*g*Depth.^2);