Error using input comand

Hey

Im struggeling to use the input command when solving an equation using the Newton Raphson method. my whole code is as follow;

clear all

close all

clc

a=input((0.5)*x^3 -3*x^2 +3*x -4,'x');

x(1)=input(4);

error=input(1);

f=inline(a)

dif=diff(sym(a));

d=inline(dif);

for i=1:100

x(i+1)=x(i)-((f(x(i))/d(x(i))));

err(i)=abs((x(i+1)-x(i))/x(i));

if err(i)<error

break

end

end

root=x(i)

when I enter;

• a=input((0.5)*x^3 -3*x^2 +3*x -4,'x');

I recieve the following error;

• Undefined function or variable 'x'.

If i define X before hand i recieve this error;

• Error using inputThe first argument to INPUT must be a string.

if i use;

• a=@(x) input((0.5)*x^3 -3*x^2 +3*x -4,'x');it brings up the same error but for the x(1) line

it would be very helpful to know why this happens and how to fix the code

thanks

sandy

[Vaclav Rimal]

What do you expect your first input command would return? The way you write your code does not make any sense; input takes just the string as an arguments.

Answer 1

[Stalin Samuel]

• Are you expecting like this

clear all

close all

clc

a='(0.5)*x^3 -3*x^2 +3*x -4';

x=input('Enter th x vector');%e.g[2 4 5 56 6 3]

error=input('Enter the error limit');%e.g  2

f=inline(a)

dif=diff(sym(a));

d=inline(dif);

for i=1:100

x(i+1)=x(i)-((f(x(i))/d(x(i))));

err(i)=abs((x(i+1)-x(i))/x(i));

if err(i)<error

break

end

end

root=x(i)

[Stalin Samuel]

Newton Raphson MATLAB Program

[sandy Fleming]

Ive tried exactly what you said but i still get an error at the line

X=input(0.5 -3 3 -4)

the 3 is underlined in red with the error; unexpected matlab expression appearing in the command window.

[Stalin Samuel]

X = [0.5 -3 3 -4] .no need to use the command input