Why doesn't my figure(2) display anything?

Hi! Badly need help with this one.. I can't get my second figure to display anything ><

%problem: f(x)= -3x^4 + 10x^2 - 3
%one plot for   -4 <= x <= 3 and another for -4 <= x <= 4

clc;
x = [-4:1:3];
y = -3*x.^4+10*x.^2-3;
a = [-4:1:4];
b = -3*x.^4+10*x.^2-3;


figure(1)
plot(x,y), xlabel('x ->'), ylabel('y ->'), title('plot for -4 <= x <= 3');

figure(2)
plot(a,b), xlabel('x ->'), ylabel('y ->'), title('plot for -4 <=x <= 4');

Answer 1

[Star Strider]

Either re-define ‘a’ or make ‘b’ a function of ‘a’ instead of ‘x’.

%problem: f(x)= -3x^4 + 10x^2 - 3
%one plot for   -4 <= x <= 3 and another for -4 <= x <= 4

clc;
x = [-4:1:3];
y = -3*x.^4+10*x.^2-3;
a = [-4:1:4];
a = linspace(min(a), max(a), numel(x))                  % Re-Define 'a' To Be The Same Size As 'x'

a = 1×8

-4.0000 -2.8571 -1.7143 -0.5714 0.5714 1.7143 2.8571 4.0000

b = -3*x.^4+10*x.^2-3;


figure(1)
plot(x,y), xlabel('x ->'), ylabel('y ->'), title('plot for -4 <= x <= 3');

figure(2)
plot(a,b), xlabel('x ->'), ylabel('y ->'), title('plot for -4 <=x <= 4');

.

[Zzahng Cal]

i see... thank you so much!!

[Star Strider]

As always, my pleasure!

Answer 2

[Simon Chan]

Variable x has 8 numbers while variable a has 9 numbers.

However, Variable y and b are calculated based on the value of variable x, so they have 8 numbers as well.

When you plot figure(2), you are going to plot variable b vs variable a and they are not the same length. As a result, an error occurs and hence it does not plot anything for you.

Just change the following line and you should be able to get a plot becasue they are now having same length.

b = -3*a.^4+10*a.^2-3;

[Zzahng Cal]

Thank you!! ^^