Finding the x interval for when a function is less than another

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PJ
PJ 2018-1-23
回答： Jordy Jose 2018-1-31
I plotted two functions 'phi' and 'RHS' and I am trying to figure out how to find the x intervals for when 'phi' is less than or equal to 'RHS'. Is there a simple code that would directly give me the x intervals and possibly highlight them on the plot.
clear all;
clc;
x=-1:0.01:5;
y=x.*(x-2).*(x-4).^2;
dy=4*x.^3-30*x.^2+64*x-32;
a=0:0.01:5;
phi= a.^4 - 10.*a.^3 +32.*a.^2 -38.*a+15;
dphi=4.*a.^3 -30.*a.^2 +64.*a -38;
c1=0.01;
figure(1)
plot(x,y)
RHS= 15 - c1.*a.*38;
figure(2)
plot(a,phi,a,RHS)

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回答（1 个）

Jordy Jose
Jordy Jose 2018-1-31
Hello,
To find the intervals of x where 'phi' is less than or equal to 'RHS', you may use "find" function. For example:
>>inds = find(phi <= RHS);
>>a(inds)

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