Why vector don't equal when differentiating sin(pi*x)

I don't understand why i keep getting : Error using plot vector must be the same length.

As the data shows s1= 1X100and s2=1X99 which i don't understand why it has that data.

clc;
sym('x');
s= sin(pi*x);
x= linspace(0,4);

subplot(2,1,1);
plot(x,s);
axis([0 4 -4 4]);

subplot(2,1,2);
s1= diff(s);
plot(x,s1)%Error at this line

Answer 1

[madhan ravi]

see subs() (link) to better understand

x= linspace(0,4);
s= sin(pi*x);
subplot(2,1,1);
plot(x,s);
axis([0 4 -4 4]);
subplot(2,1,2);
syms x
s1= diff(sin(pi*x),x);
x= linspace(0,4);
plot(x,subs(s1,x))

[Nam Nguyen]

Thank you

[madhan ravi]

Anytime :)

Answer 2

[KSSV]

YOu have to substitue the value of x in the sym objects s and s1 using subs. After that it will be converted to double and then you can plot them.

syms x;
s= sin(pi*x);
x= linspace(0,4);
subplot(2,1,1);
sr = subs(s,x) ;
plot(x,sr);
axis([0 4 -4 4]);
subplot(2,1,2);
s1= diff(s);
s1r = subs(s1,x) ;
plot(x,s1r)%Error at this line

Answer 3

[KSSV]

YOu need not to use sums actually. Using syms is useless in your case.

x= linspace(0,4);
s= sin(pi*x);
subplot(2,1,1);
plot(x,s);
axis([0 4 -4 4]);
subplot(2,1,2);
s1= gradient(s);
plot(x,s1)%Error at this line