inline function and convert

Question is that:

Create an m-file that asks for a function (sin(x) + cos(3*y) ....) that depends on different variables x,y and z or like the one in problem 1.Your m-file should localize y and z and then switch these against x. Plot the the new function versus x. Where x=0:0.1:20.

my code:

fnc=input('Enter any function with three variables:','s');

g=inline(fnc);

disp(g)

x=0:0.1:20;

plot(x,g,'r--','linewidth',2);

xlabel('x axis')

ylabel('y axis')

I want from user to enter 3 variable function and then plot it as single variable but it gives an error like that:

Error using ==> plot
Conversion to double from inline is not possible.

Error in ==> assignment3 at 11

plot(x,g,'r--','linewidth',2);

title('x versus '+ fcn);

what is the problem :s

Thank you very much for your kind answers.

Yahya Aktaş

[SL: formatted question as text not code]

Answer 1

[Rupesh]

Hi Yahya,

    I understand that you're looking to input a function involving three variables (x, y, z), convert it into a single-variable function by substituting y and z with x, and then plot this function over a specified range of x values. You've encountered an error due to directly attempting to plot an inline function object, which MATLAB cannot process as expected. To address your issue, I have made some small modifications to the code to get the desired results.

function plotUserFunction 
% step 1Prompt the user for a function involving x, y, z 
userFunc = input('Enter any function with variables x, y, and z: ', 's'); 

% step 2 Convert the User-inputted Function: Use MATLAB's ability to handle strings and convert them into anonymous functions. 
% Substitute Variables: Directly replace y and z with x in the user's input. 
modifiedFunc = strrep(strrep(userFunc, 'y', 'x'), 'z', 'x'); 

%step 3  Convert the modified function string into an anonymous function 
g = @(x) eval(vectorize(modifiedFunc)); 

% Define the range of x 
x = 0:0.1:20; 

% step 4Evaluate the Function: Use MATLAB's vectorized operations to evaluate the newly created single-variable function over the specified range of x values. 
y = arrayfun(g, x); 

% Step 5 Plot the Fun: Plot the evaluated function values against x 
figure; plot(x, y, 'r--', 'LineWidth', 2); 
xlabel('x axis'); ylabel('y axis'); 
title('Plot of the modified function'); 
end  

As you can observe in the above code, a key aspect of achieving the solution involves the use of MATLAB's vectorized operations to evaluate the newly created single-variable function across the specified range of x values. This is done through the line fourth step, which applies the function `g`—our single-variable function—to each element within the array of x values.

You can refer to the below doc for a better understanding of the arrayfun function used in the above script.

https://www.mathworks.com/help/matlab/ref/arrayfun.html

Hope it helps!