range in fplot as variables

clear
clf
clc
syms x y
f=x*y*(x+y);
ylim=[x^2 x];
ylow=ylim(1);
yup=ylim(2);
sol=solve(ylim(1)==ylim(2),x);
a=sol(1);
b=sol(2);
xlim=[a b];
integral=int(int(f,y,ylim(1),ylim(2)),x,xlim(1),xlim(2));
disp('The integral of f in the region enclosed is')

The integral of f in the region enclosed is

disp(integral)

fplot(ylow,[a b])
hold on
fplot(yup)
for p=xlim(1):0.01:xlim(2)
    line([p p],subs(ylim,x,p),'Color','#abdbd4')
end

Warning: Error updating ParameterizedFunctionLine.

The following error was reported evaluating the function in FunctionLine update: Non-scalar in Uniform output, at index 1, output 1.
Set 'UniformOutput' to false.

Error using plot
Vectors must be the same length.

hold off

the job is pretty simple i want to show the regio of integration for a double integral in order dx dy

i have to generalize the above code for any function so that range in fplot should [a b]

although when i run the code it gives me this error

apparently if i give the range as [0 1]

it has no issues

but not all functions will have integrating region in a specific range say [0 5] (default)

why doesn't fplot takes [a b] as the range

Answer 1

[VBBV]

clear
clf
clc
syms x y
f=x*y*(x+y);
ylim=[x^2 x]

ylim = 

ylow=ylim(1);
yup=ylim(2);
sol=solve(ylim(1)==ylim(2),x)

sol = 

a=sol(1);
b=sol(2);
xlim=[a b];
I=int(int(f,y,ylim(1),ylim(2)),x,xlim(1),xlim(2));
disp('The integral of f in the region enclosed is')

The integral of f in the region enclosed is

disp(I)

fplot(ylow,[0 5])
hold on
fplot(yup,[0 5])  % specify the same range 
axis([0 5 0 5])
for p=xlim(1):0.01:xlim(2)
    line([p p],[subs(ylim,x,p)],'Color','red')
   
end
hold off

figure 
for p=xlim(1):0.01:xlim(2)
    line([p p],[subs(ylim,x,p)],'Color','red')
   
end