Input Function of (x,y) For Loop Error

i'm trying to input function of x,y

dy =  input ('dy/dx =  ','s');
dy = @(x,y) dy;

and also try

dy =  input ('dy/dx =  ','s');
dy = inline(dy);

then make a for loop to calculate y(2) based on the value of y(1) and dy(1) ===> which a function x,y

for o = 1 : 1 : n
    y(o+1) =  y(o) + delx * dy(x(o),y(o));
    dy(o+1) = feval(dy,x,y);
end

here I want to use the just calculated y(2) to calculate the value of dy(2) and when run that code give me that error

In an assignment  A(:) = B, the number of elements in A and B must be the same.

Error in Final (line 500)
    y(o+1) =  y(o) + delx * dy(x(o),y(o));

===================================================

update:

thank you (@Walter Roberson)

this help in convert the string to function

still there that error

Not enough input arguments.

when enter the for loop

for o = 1 : 1 : n
  y(o+1) =  y(o) + delx * dy(x(o),y(o));
  dy(x(o+1),y(o+1)) = feval(dy(o),x(o),y(o));
end

and when made it

for o = 1 : 1 : n
  y(o+1) =  y(o) + delx * dy(x(o),y(o));
  dy(o+1) = feval(dy,x,y);
end

the error is

Matrix dimensions must agree.

Error in Final>@(x,y)x-y

Error in Final (line 500)
    dy(o+1) = feval(dy,x,y);

Answer 1

[Walter Roberson]

dy_string =  input ('dy/dx =  ','s');
dy = str2fun( ['@(x,y) ', dy_string] );

[king zogorn]

thank you @Walter this help in convert the string to function

still there that error

Not enough input arguments.

when enter the for loop that when make the loop like that

for o = 1 : 1 : n
  y(o+1) =  y(o) + delx * dy(x(o),y(o));
  dy(x(o+1),y(o+1)) = feval(dy(o),x(o),y(o));
end

and when made it

for o = 1 : 1 : n
  y(o+1) =  y(o) + delx * dy(x(o),y(o));
  dy(o+1) = feval(dy,x,y);
end

the error was

Matrix dimensions must agree.

Error in Final>@(x,y)x-y

Error in Final (line 500)
    dy(o+1) = feval(dy,x,y);

[Walter Roberson]

dy(x,y)

with no feval.

However, do not assign the output to dy(o+1) . dy is a function handle . If you need a record of the output of the function, use a different variable.

y(o+1) = y(o) + delx * dy(x(o), y(o));
dy_val(o+1) = dy(x(o), y(o+1));

However you need to think about whether the second dy calculation should use x(o) or x(o+1)