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

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Zzahng Cal on 29 Mar 2022
Commented: Zzahng Cal on 29 Mar 2022
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');

Star Strider on 29 Mar 2022
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'); .
##### 2 CommentsShowHide 1 older comment
Star Strider on 29 Mar 2022
As always, my pleasure!

Simon Chan on 29 Mar 2022
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 on 29 Mar 2022
Thank you!! ^^