# Write a function max_sum that takes v a row vector of numbers & n,a positive integer as inputs.The function needs to find n consecutive elements of v whose sum is largest possible.It returns summa & index of first element of n consecutive integers.

145 visualizzazioni (ultimi 30 giorni)
vidushi Chaudhary il 19 Mag 2020
Commentato: khalid il 14 Lug 2023
%Example-[summa,index]=max_sum([1 2 3 4 5 4 3 2 1],3)
% summa=13
% index=4
function [summa,index]=max_sum(v,n)
total=v(1,1);
if n>v
summa=0;
index=-1;
else
for ii=1:length(v)
jj=ii+(n-1);
if jj<=length(v);
total=[total,sum(v(ii):v(jj))];
end
[summa,index]=max(total);
end
end
##### 12 CommentiMostra 10 commenti meno recentiNascondi 10 commenti meno recenti
Vivek Mishra il 23 Gen 2022
would you please explain the line : total=v(1,1); and total=[total,sum(v(ii):v(jj))];
khalid il 14 Lug 2023
function [summa,index]=max_sum(v,n)
summa=1;
c=size(v,2);
p=0;
if(n<=c)
for jj=1:(c-n+1)
s=0;
for ii=jj:jj+n-1
s=s+v(1,ii);
end
p = v(1,jj);
if(s>summa)
summa=s;
index=p;
end
end
else
summa = 0;
index =-1;
end
end

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### Risposta accettata

KSSV il 19 Mag 2020
Modificato: KSSV il 19 Mag 2020
v = [1 2 3 4 5 4 3 2 1] ;
n = 3 ;
N = length(v) ;
sumn = zeros(1, N - n + 1); % Pre-allocation
for i = 1:N - n + 1
sumn(i) = sum(v(i:(i+n-1))) ;
end
[val,idx] = max(sumn)
##### 22 CommentiMostra 20 commenti meno recentiNascondi 20 commenti meno recenti
sumit amanagi il 6 Ago 2021
what min(ind) does?
Walter Roberson il 6 Ago 2021
There is a possibility that there is more than one location that is the maximum. The find() step returns all of the locations and min() of the find returns the first. Another way of doing that would be to use find(Summa==S, 1)

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### Più risposte (22)

Willynx Vixamar il 13 Nov 2020
function [summa, index] = max_sum(v,n)
L = length(v);
S=zeros(1,L-n+1);
if n > L
summa = 0;
index = -1;
return
else
for i = 1:(L-n+1)
S(i)=sum(v(i:(i+n-1)));
end
summa = max(S);
ind = find(S == summa);
index = min(ind);
end
end
##### 6 CommentiMostra 4 commenti meno recentiNascondi 4 commenti meno recenti
MINH il 30 Giu 2023
Can somebody help me explain this part of the code :
ind = find(S == summa);
index = min(ind);
Cheers,
DGM il 30 Giu 2023
Modificato: DGM il 30 Giu 2023
The first line returns the linear indices of S where S==summa.
The second line returns the minimum of those indices.
Both lines are unnecessary, because max() will return that index if you actually request it. Why do all this:
summa = max(S);
ind = find(S == summa);
index = min(ind);
... when you can just do:
[summa index] = max(S);

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Rik il 6 Lug 2020
Modificato: Rik il 30 Lug 2020
You can get a speedup by using a convolution to calculate the moving sum:
v=randi(100,2000,1);
n=10;
clc
timeit(@() option1(v,n))
ans = 3.4287e-04
timeit(@() option2(v,n))
ans = 3.5765e-05
function [val,idx]=option1(v,n) % function as suggested by KSSV
N = length(v) ;
sumn = zeros(1, N - n + 1); % Pre-allocation
for i = 1:(N - n + 1)
sumn(i) = sum(v(i:(i+n-1))) ;
end
[val,idx] = max(sumn);
end
function [val,idx]=option2(v,n)
if n>numel(v),val=0;idx=-1;return,end
sumn=conv(v,ones(n,1),'valid');
[val,idx] = max(sumn);
end
##### 1 CommentoMostra -1 commenti meno recentiNascondi -1 commenti meno recenti
DGM il 8 Mar 2023
Modificato: DGM il 8 Mar 2023
Edited only to demo the code.
An order of magnitude improvement and it's nice and concise -- what's not to like?

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Bruno Luong il 29 Lug 2020
Modificato: Bruno Luong il 29 Lug 2020
N=3;
v = [1 2 3 4 5 4 3 2 1];
[s,index] = maxsum(v, N)
Using this function
%% NOTE this function returns empty outputs if N>length(v)
% might be more sensitive to numerical error
function [s,index] = maxsum(v, N);
c=cumsum([0; v(:)]);
[s,index]=max(c(N+1:end)-c(1:end-N));
end
Result
s =
13
index =
4
>>
##### 4 CommentiMostra 2 commenti meno recentiNascondi 2 commenti meno recenti
Rik il 30 Lug 2020
Thanks for the correction. I tested it for random lengths random vectors with random N against your code, and it seems to match now.
The fix doesn't affect the timing.
Bruno Luong il 30 Lug 2020
Modificato: Bruno Luong il 30 Lug 2020
The faster timing of CONV for large array can be perhaps explained by multi-thread of the engine, that cannot be carrierd out with CUMSUM, which is sequential calculation.
TMW comes from far, the CONV in the earlier years suffered from performance. Now they have improved it greatly.
In any case a factor of 0.7 1.5 between two methods are to me essentially ... 1.
In any case your code get a vote from me.

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Bruno Luong il 1 Ago 2020
function [s,index] = maxmovsum(v, N)
c = movsum(v,N);
[s,index] = max(c(1+floor(N/2):end-floor((N-1)/2)));
end
##### 0 CommentiMostra -2 commenti meno recentiNascondi -2 commenti meno recenti

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tharak infinity il 10 Nov 2020
function [summa, ind] = max_sum(v,n)
% If n is greater than v return the specified values
% Using return keyword exits the function so no further code is
% evaluated
if n > length(v)
summa = 0;
ind = -1;
return;
end
% Initialize summa to -inf.
% Then work through the vector, checking if each sum is larger than the
% current value of summa
summa = -inf;
ind = -1;
% Once we get to length(v)-n+1 we stop moving through the vector
for ii = 1:length(v)-n+1
currentV = v(ii:(ii+n-1));
currentSumma = sum(currentV);
% If currentSumma greater than summa, update summa and ind
if currentSumma > summa
summa = currentSumma;
ind = ii;
end
end
end
##### 3 CommentiMostra 1 commento meno recenteNascondi 1 commento meno recente
OUSSAMA El GABBARI il 24 Gen 2022
Could you explain the summa = -inf; line ?
Is -inf a built in keyword or something ?
Rik il 24 Gen 2022
inf is the keyword for infinity. Negative infinity is guaranteed to be the lowest value possible.

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Sahil Deshpande il 17 Dic 2020
function [summa,index] = max_sum(v,n)
l=length(v);m=0;t=0;pointer=1;index=0;
%When n is larger than the length of vector v
if n>l
summa=0;
index=-1;
else
%When n is smaller than the length of vector
for a = 1:n
m=m+v(a);
end
for i = 1:(l-(n-1))
k=i;t=0;
for j = 1:n
t = t+v(k);
k=k+1;
end
if t>m
m=t;
pointer=i;
end
end
summa=m;
index=pointer;
end
I have written this code without using any inbuilt functions, just using loops. It works great!
I know it looks kinda ugly, can anyone help me optimize this code and make it shorter?
##### 1 CommentoMostra -1 commenti meno recentiNascondi -1 commenti meno recenti
Rik il 17 Dic 2020
Have you looked at the other solutions in this thread?
Also, you already used a builtin function on your first line: length.

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Shantanu Nighot il 22 Dic 2020
% Here is the working code for This Problem statement
function [summa index] = max_sum(v,n)
ii = 1;
jj = n;
% Initialize summa to zero
summa = 0;
% if n is greater than number of elements in v the return summa = 0, index = -1
if n>numel(v)
summa = 0;
index = -1;
% pro tip
% If n is equal to number of elements in v then index will always be 1 and summa = sum(v(ii:jj))
elseif n==numel(v)
summa = sum(v(ii:jj));
index = 1;
else
% while loop for calculating the sum of n elements of subsequence of v
while jj<=numel(v)
% If sum of n elements of subsequence of v is greater than the previous one
% then that sum is stored in summa and index of first element is stored in index
if sum(v(ii:jj))>summa
summa = sum(v(ii:jj));
index = ii;
end
if sum(v(ii:jj))<0 && summa == 0
summa = sum(v(ii:jj));
index = ii;
end
ii = ii + 1;
jj = jj + 1;
end
end
##### 0 CommentiMostra -2 commenti meno recentiNascondi -2 commenti meno recenti

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Ali Mohammadi il 21 Ott 2021
and this is my solution for it:
function [summa, index] = max_sum(v, n)
%creat an empty vector for cunsecutive sums, and ultimately determine the
%highest value and its index with max(w)
w = [];
ii = 1;
if n > length(v)
summa = 0
index = -1
return;
else
while n <= length (v)
w(ii) = sum(v(ii:n));
ii = ii + 1;
n = n + 1;
end
[summa, index] = max(w)
end
%I have checked, it works :)
##### 1 CommentoMostra -1 commenti meno recentiNascondi -1 commenti meno recenti
Rik il 21 Ott 2021
What's the point of adding yet another solution? This isn't Cody.

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Eric il 22 Lug 2020
Modificato: Eric il 22 Lug 2020
I came up with a function that, I think, accomplishes this task. It runs fine in my MATLAB (2020a). However, it doesn't seem to be acceptable in the Assignment Submission. Anyone know why this could be the case?
function[summa,index]=max_sum(v,n)
if n>length(v)
index=-1;
summa=0;
else
sumn=movsum(v,n);
[summa,index]=max(sumn);
index=index-1;
end
end
##### 5 CommentiMostra 3 commenti meno recentiNascondi 3 commenti meno recenti
Eric il 23 Lug 2020
Sorry, not logical indexing. That would be "normal" indexing, right? [summa,index]=max(sumn) gives the maximum and index of that (middle) value in the vector sumn. The next line changes that index to the first value in that rolling sum. When running the code with my debugger, it seems to work with a range of values.
TANUJA GUPTA il 29 Lug 2020
@Eric, Actually when we type for example [summa,index] = max(sum); it gives the maximum value which is passed to summa, but in index it passes the index of the first no.
[Y,I] = max(X) returns the indices of the maximum values in vector I.
If the values along the first non-singleton dimension contain more
than one maximal element, the index of the first one is returned.

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Capulus_love il 11 Ago 2020
Modificato: Capulus_love il 11 Ago 2020
%why second problem doesn't run?
function [summa,index] = max_sum(v,n)
s = size(v); b = 0; c = 0; index = 0;
if s(2) < n
index = s(2) - n;
summa = 0;
return
end
for i = 1:s(2)-n+1
c = sum(v(i:i+n-1));
if c > b
b = c;
index = i;
else
b = b;
end
end
summa = b;
end
%Variable ind has an incorrect value.
% max_sum([ -66 31 61 60 -70 7 9 0 8 90 -54 72 12 ...
% 89 -50 4 86 -3 83 -52 ], 23) returned sum = 0 and index = -3 which is incorrect...
##### 3 CommentiMostra 1 commento meno recenteNascondi 1 commento meno recente
Capulus_love il 11 Ago 2020
in my matlab program,, it returns
summa =0
index = -3
with upper problem.
I'm not sure which part is not solved.
Did I not understand the problem?
Rik il 11 Ago 2020
Put a breakpoint on the first line. Then use the debugger to execute your function line by line. When do you see the index go negative? When do your variable get unexpected values?
When you do that you will notice that your assumption of a column vector input isn't enforced anywhere.

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LEE MUN LING il 18 Dic 2020
function [m k]=max_sum(v,n)
m=0;
if n>length(v)
k=-1;
m=0;
return
else
for k=1:((length(v)-n)+1);
while m<max(sum(v(k:((n-1)+k))));
m=max(sum(v(k:((n-1)+k))));
m=m;
k=k;
end
end
end
##### 2 CommentiMostra NessunoNascondi Nessuno
LEE MUN LING il 18 Dic 2020
Can you guys help me check for this,
I try several time inserting the break statement in the loop but the iteration still continues, it is suppose to stop at k=4 when my input argument is ([1 2 3 4 5 4 3 2 1],3)
Rik il 18 Dic 2020
m=m; and k=k; will not do anything, so why are they in your code? Also, you posted this as an answer, but it is a question. (and you forgot to format your code as code)
Are you aware that break will only stop one loop, not all? And have you looked at the other solutions in this thread?

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Rahil Ginwala il 23 Dic 2020
function [summa, index] = max_sum(v,n)
summa = 0;
i = 0;
j = v;
m = [];
c = 1;
if n>v
summa=0;
index=-1;
else
while i < n
c = numel(v(v==max(j))); % number of times the element is in the array
summa = summa + max(j)*c; % multiplying by c
b = find(v==max(j)); % find the max elemnets of v
m = [m b];% array of positions with max element
j = j(j<max(j));% remove the max number from array
i = i + 1;
end
t = sort(m);
index = t(1,1)
end
% I am not able to stop i from goigng to value 3 which gives the error for sum and index
##### 1 CommentoMostra -1 commenti meno recentiNascondi -1 commenti meno recenti
Rahil Ginwala il 23 Dic 2020
How Can I correct this error?

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Abhishek Sharma il 28 Gen 2021
% tbh, I used some help from these forum answers too
function [summa,index]=max_sum(v,n)
% first checking whether the size of row vector v is less than n or not
% if yes then print according to the given statement
if n>length(v);
summa=0;
index=-1;
else
% so you are thinking about why i took (-n+1) right?
% think of a value of size of row vector v and n
% you will get to know the answer by yourself ,example take size of v= 10 & n=10
for i=1:(length(v)-n+1);
mysum(i)=sum(v(i:i+n-1));
end
summa=max(mysum);
% I couldn't find this one, hence i used the help of this forum
x=find(mysum==summa);
index=min(x);
end
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Daniel Anaya il 9 Apr 2021
%i dont know what to do. my works pretty good with positive integers. I dont know wht it has errors with negative integers
function [summa, index] = max_sum(v,n)
summa = 0;
ii = 1;
jj = n;
total = [];
if n > numel(v)
summa = 0;
index = -1;
elseif n == numel(v)
summa = sum(v(ii:jj));
index = v(1,1);
elseif n < numel(v)
for ii = 1:numel(v)
jj = ii + (n - 1);
if jj <= numel(v);
total = [total, sum(v(ii:jj))];
end
end
summa = max(total);
x = find(total == summa);
index2 = min(x);
index = v(index2);
end
##### 3 CommentiMostra 1 commento meno recenteNascondi 1 commento meno recente
Daniel Anaya il 9 Apr 2021
Modificato: DGM il 22 Gen 2023
function [summa, index] = max_sum(v,n)
summa = 0;
ii = 1;
jj = n;
total = [];
if n > numel(v)
summa = 0;
index = -1;
elseif n == numel(v)
summa = sum(v(ii:jj));
index = 1;
elseif n < numel(v)
for ii = 1:numel(v)
jj = ii + (n - 1);
if jj <= numel(v);
total = [total, sum(v(ii:jj))];
end
end
summa = max(total);
x = find(total == summa);
index = min(x);
end
Jasmine il 18 Gen 2023
Modificato: Jasmine il 18 Gen 2023
it worked for me thank you

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Shun Yan il 16 Apr 2021
function [a,b]=max_sum(A,B)
n=1;
C=0;
for ii = 1:(size(A,2)-B+1)
C(n)=sum(A(n:(B+n-1)));
n=n+1;
end
if B>size(A,2)
a=0;
b=-1;
else
a=max(C);
b=find(C==max(C));
end
I don't get what is variable ind, and how's sum 4 index9 wrong; can someone pls help? Thanks!
##### 2 CommentiMostra NessunoNascondi Nessuno
Rik il 16 Apr 2021
What happens when you try this input to your function?
[a,b]=max_sum([1 2 3 4 5 4 3 2 1],2)
a = 9
b = 1×2
4 5
Is that correct? How can the index (the second output) be multiple values?
function [a,b]=max_sum(A,B)
n=1;
C=0;
for ii = 1:(size(A,2)-B+1)
C(n)=sum(A(n:(B+n-1)));
n=n+1;
end
if B>size(A,2)
a=0;
b=-1;
else
a=max(C);
b=find(C==max(C));
end
end
Shun Yan il 16 Apr 2021
Thanks!!

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Giancarlo milon il 29 Giu 2021
function [summa,index] = max_sum(v,n)
b=1;
summa = -1000000;
%i start it with -1000000 because you ALWAYS want to overwrite your summa
index = 0;
if n > size(v)
summa = 0;
index = -1;
return
else
%this if checks for size condition if n is bigger than the size summa is 0
%and index -1
while n<=length(v);
%this will break when n = to lenght of the vector
if sum(v(b:n)) > summa
%this condition sets the sumatory of the position from b to n.
%In this case b starts in 1 and n is the input, if the sum is
%bigger than the summa it overwrites it, thats why we wanted
%always to overwrite the value summa and we started it with
%-1000000
summa = sum(v(b:n));
index = b;
end
b = b+1;
n = n+1;
%adds +1 to b and n so my positions go from 1:n to 2:n+1 to 3:n+2
%till n = the lenght and it stops
end
end
##### 3 CommentiMostra 1 commento meno recenteNascondi 1 commento meno recente
Giancarlo milon il 23 Lug 2021
the variable double has a max min number, idc wich is it. But u can change the -1000000 for that max min number that the memory can hold in the variable if u want. that should solve it. if ur input is that max min number u can add a counter of times the summa it equal to the starting number, save that position and return that position
Rik il 23 Lug 2021
Your function should handle such a case. If the user needs to know how your function works and might need to edit your function, then it isn't working well.
Such limitations should be mentioned in the documentation of your function (which it currently lacks).
If you want to overwrite a variable with the lowest possible value, you should replace it with -inf.
%the number you were looking for is this:
-realmax
ans = -1.7977e+308

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Ujwal Dhakal il 6 Gen 2022
function [summa, index] = max_sum(v,n)
a=length(v);
sumvar=zeros(1,a-(n-1)); %preallocating a vector (you can skip this for now_go ahead and read the rest of the code)
%for invalid input
if n>a
summa=0;
index=-1;
return;
end
%assume a matrix on your own and try running i and j using the formula below, you'll get it
for i=1:(a-(n-1))
sumtemp=0;
for j=i:(n+i-1)
sumtemp=sumtemp+v(j);
end
sumvar(i)=sumtemp;%takes the sum and catenates into a vector sumvar _ that was preallocated to save some computational time
end
[summa,index_temp]=max(sumvar(:)); % if you give two output arguments to a max function, the second argument returns index of that element
index=index_temp; % the index of the maximum number in the vector sumvar happens to be also the index of our first number in the sequence
end
##### 0 CommentiMostra -2 commenti meno recentiNascondi -2 commenti meno recenti

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Yifan He il 27 Lug 2022
function [summa,index] = max_sum(v,n)
if n > length(v)
summa = 0;
index = -1;
end
if n <= length(v)
summa = sum(v(1:n));
index = 1;
for i = 1:length(v)-n
if sum(v(i+1:i+n)) > summa
summa = sum(v(i+1:i+n));
index = i+1;
else
continue;
end
end
end
##### 0 CommentiMostra -2 commenti meno recentiNascondi -2 commenti meno recenti

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function [summa,index]=max_sum(v,n)
Z=length(v);
summ=(1:Z-n+1);
if n>Z
summa=0;
index=-1;
return;
else
for i=1:(Z-n+1)
summ(i)=sum(v(i:(i+n-1)));
end
end
[summa,index]=max(summ);
##### 0 CommentiMostra -2 commenti meno recentiNascondi -2 commenti meno recenti

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Nyeche il 23 Ott 2022
function [summa, index] = max_sum (v, n)
if n < 0 || n ~= fix(n) || ~isrow(v)
error('Input must be an integer');
elseif n > length(v)
summa = 0;
index = -1;
end
total = 0;
l = length(v);
for i = 1:l-(n-1)
total(i) = sum(v(i:i+(n-1)));
summa = max(total);
index_1 = find(total == summa);
index = min(index_1);
end
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Boran Yigit Usta il 16 Nov 2022
function [summa,index] = max_sum(v, n)
b = zeros(1,n);
a = find(v == max(v));
for ii = 1:n
b(ii) = max(max(v));
if find(v==b(ii),1) < a
a = find(v==b(ii),1);
end
v(find(v==max(v),1)) = 0;
end
if n > length(v)
summa = 0;
index = -1;
else
summa = sum(b);
index = a;
end
##### 1 CommentoMostra -1 commenti meno recentiNascondi -1 commenti meno recenti
Boran Yigit Usta il 16 Nov 2022
i tested it it with variety of inputs and it works but still i get this error;
Assessment result: incorrectrandom vectors
Variable summa has an incorrect value. max_sum([ 53 -40 60 -76 -18 31 -61 67 60 75 -60 -2 60 51 -54 -10 -4 -48 -39 80 90 96 53 88 ], 5) returned sum = 429 and index = 10 which is incorrect...

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Modificato: DGM il 5 Mar 2023
function [summa,index]=max_sum(v,n)
len=length(v); %v的長度
if(n>length(v)) %n大於v的長度
summa=0;
index=-1;
return;
else
temp_sum=zeros(1,len-n+1);
for x=1:len-n+1
temp_sum(x)=sum(v(x:x+n-1));
end
[summa,index]=max(temp_sum);
end
end % end of function
##### 1 CommentoMostra -1 commenti meno recentiNascondi -1 commenti meno recenti
DGM il 5 Mar 2023
Modificato: DGM il 5 Mar 2023
Still very samey ...

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