If I understand correctly, you only wish to plot I as a function of x.
I have modified your function slightly (at the end of the code), including some semicolons to make it less talkative.
% Make a vector of I values
I_x = linspace(100e6,450e6,1000);
% Set constants
v=-0.7;
x0=500;
q0=1;
L=1000;
E=140;
% Preallocate x vector for speed
x_x = zeros(size(I_x));
% Repeatedly call the function, assigning the result to an element of the
% x_x vector
for idx = 1:numel(I_x)
x_x(idx) = beam2(x0,q0,v,L, I_x(idx) ,E);
end
% Plot
hold on
title ('I as a function of x')
xlabel('x[mm]')
ylabel('I[mm]')
plot(x_x,I_x)
hold off
% Your function
function X_coordinate = beam2(x0,q0,v,L,I,E)
epsilon = 1e-4;
flag = 0;
counter = 0;
x=x0;
while flag == 0
%Check for infinite loop
counter = counter + 1;
if counter > 10000
error('Too many iterations');
end
F = -(q0*L)/(3*pi^4*E*I)*(48*L^3*cos((pi*x)/(2*L))-48*L^3+3*pi^3*L*x^2-pi^3*x^3)-v;
F_d = -(q0*L)/(3*pi^4*E*I)*(-48*L^3*(pi/(2*L))*sin((pi*x)/(2*L))+6*pi^3*L*x-3*pi^3*x^2);
x = x-F/F_d; %solution
if abs(F/F_d) < epsilon || abs(F) < epsilon
flag = 1;
end
end
X_coordinate = x;
if X_coordinate <=0 || X_coordinate > 1000
error('No solution found,Please enter valid value')
else
X_coordinate = x;
end
end
