Asked by Rongyu Chu
on 14 Oct 2019

Hi, guys. The question I am asked to solve is like this. I will be given a list of numbers (note that the first and last numbers of this list will be equal and will be the maximum number in this list). In first step, I am asked to delete all the numbers whose value is between or equal to its adjcent numbers. For example, if the list given is [2 -1 -3 -3 2]. First -1 will be delte since its value is between 2 and -3. Then -3 will be delerte since there is another -3 on the side of it. The final list will be [2 -3 2]. Similaly, the second step asks to delte 2 numbers out of 4 if both the 2nd and 3rd numbers' value is in the middle or equal to 1st and 4th number. For example, if the list is [2 -1 -2-3]. -1 and -2 will be delete. And finally, I am asked to output the index of the numebs I delete in the second step.(Note that, the index number number should come from the very first list, not list after edit). I paste my code below. It works but will take 140s. The while loops took a lof of time to run. I am wondering if there is anyway to accelerate my code like avoiding using while loop. Thank you for your guys help. Really apperciate it.

clear all; close all; clc;

N = load('expp.dat');

N = N';

len = length(N);

B= 1:len;

judge = 1;

while judge == 1

judge = 0;

for i = 1 : len-2

if (N(i+1)-N(i+2)) * (N(i+1)-N(i)) <= 0

N=[N(1:i),N(i+2:len)];

B=[B(1:i),B(i+2:len)];

judge = 1;

break

end % if

end % for

len = length(N);

end % while

A = N;

len = length(A);

%%

m = 1;

judge = 1;

file = fopen('ans.dat','w');

while judge == 1 && len >= 4

for i = 1:(len-3)

judge = 0;

if (A(i+1)-A(i))*(A(i+1)-A(i+3)) <= 0 && (A(i+2)-A(i))*(A(i+2)-A(i+3)) <=0

if A(i+1)<=A(i+2)

C(m) = B(i + 1);

C(m + 1) = B(i + 2);

else

C(m) = B(i + 2);

C(m + 1) = B(i + 1);

end % if

fprintf(file,'%8d %8d\t\n', C(m),C(m+1));

A = [A(1:i),A(i+3:len)];

B = [B(1:i),B(i+3:len)];

m = m + 2;

judge=1;

break

end % if

end % for

len = length(A);

end % while

Answer by Rongyu Chu
on 14 Oct 2019

Is there anyway I can use matrix instead of loops ? Matrix should be able to solve this much faster.

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## 2 Comments

## darova (view profile)

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https://de.mathworks.com/matlabcentral/answers/485179-how-to-accelerate-my-code#comment_756016

## Rongyu Chu (view profile)

## Direct link to this comment

https://de.mathworks.com/matlabcentral/answers/485179-how-to-accelerate-my-code#comment_756021

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