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Write a function called max_sum that takes v, a row vector of numbers, and n, a positive integer as inputs. The function needs to find the n consecutive elements of v whose sum is the largest possible.

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Ajai Kannan
Ajai Kannan 2019-2-13
关闭： Rik ，2020-6-22
In other words, if v is [1 2 3 4 5 4 3 2 1] and n is 3, it will find 4 5 and 4 because their sum of 13 is the largest of any 3 consecutive elements of v. If multiple such sequences exist in v, max_sum returns the first one. The function returns summa, the sum as the first output argument and index, the index of the first element of the n consecutive ones as the second output.
I tried the follwing code but when there are two occurences for the same number, they both get removed in the same iteration and thus causes trouble.
function [summa, index] = max_sum(v,n)
summa = 0;
i = 0;
j = v;
m = [];
while i < n
summa = summa + max(j);
b = find(v==max(j));
m = [m b];
j = j(j<max(j));
i = i + 1 ;
end
t = sort(m);
index = t(1,1);
end
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Guillaume
Guillaume 2019-2-13
Don't use the question title to post the content of your assignment as that get truncated.
Assuming that your assigment is to find the sequence of length n of consecutive numbers with the highest sum, then I don't see how your algorithm even attempts that. You don't care about the maximum of the vector, it's completely irrevelant to the sequence sum. You want to calculate a sliding sum (i.e. first sum(v(1:n)), then sum(v(2:n+1)), etc. and find the maximum of these.
If you're allowed to use movsum, it can be trivially done in just two lines.
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Stephen23
Stephen23 2019-5-1
编辑：Stephen23 2019-5-1
@Maximilian Schmidt: movesum is called inside the function max, and it is max is called with two output arguments. So you need to read the max documentation.
A function called inside another function, like movesum inside max in your example, returns exactly one output argument as an input argument to the wrapper function, so
your example:
[summa, index] = max(movsum(h, n, 'Endpoints', 'discard'))
is exactly equivalent to
tmp = movsum(h, n, 'Endpoints', 'discard');
[summa, index] = max(tmp)

更多回答（37 个）

lalit choudhary
lalit choudhary 2019-4-17
After hours of brainstorming, i finally figured it out
try this code-
function [summa, index]=max_sum(b,n)
y=length(b)
if n>y
summa=0;
index=-1;
else
[summa, index] = max(movsum(b, n, 'Endpoints', 'discard'));
end
end
  6 个评论
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Walter Roberson
Walter Roberson 2020-5-11
When you have a vector of length nx to be taken in full windows of length n, sliding along 1 at a time, then you have nx - n + 1 full windows. For example, data = [1 2 3 4 5 6 7 8 9 10], n = 7, then nx = 10, nx - n + 1 is 10 - 7 + 1 = 4, corresponding to the windows 1:7, 2:8, 3:9, 4:10
This codes is specifically for the case where you only want full windows -- which is what the 'discard' option of movsum is intended to indicate, that you want to discard any sum that was made with a window that was not full (such as 5:10 not being the full length of 7)
Shubham Pandey
Shubham Pandey 2020-4-3
function [s,i] = max_sum(v,n)
s = 0; i = 0;
len = length(v);
l = len-n+1;
if n>len
s = 0;
i = -1;
else
for j=1:l
if j==1
s = sum(v(j:n));
i=1;
end
if s<sum(v(j:n))
s = sum(v(j:n));
i = j;
end
if n<len
n=n+1;
end
end
end
end
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Prasad Reddy
Prasad Reddy 2020-4-14
function [summa,index] = max_sum(v,n) % defining a function with name "max_sum", input augements are (v,n) and out put augemnts are [summa,index]
[r,e]=size(v); % reading the size of vector "v" to "r,e"
summa=0; % asaining 0 to summa
index=-1; % assaining -1 to index, as they asked in the question
sums=zeros(1,e-(n-1)); % creating a zro vector of requirted size. you can try itby taling two or th trial cases
if n>e % checking if n is greatr than th length of the vector so that summa and index can be rturnd as
summa=summa; % 0 and -1 respectively as askeed in the question.
index=index;
else % if n is less than the length of vctor then
for i=1:e-(n-1) % for loop to run across the length of the vector
for j=0:n-1 % for loop to run across the required number of elements to be summed
sums(i)=sums(i)+v(i+j); % elments of sums which are initially zeros are being updated step by step with th sum of 'n' numbers in vector
end
end
[s,i]=max(sums); % reading th maximum valu and its indx from sums to 's' and 'i'
summa=s;
index=i;
end
end
asad jaffar
asad jaffar 2019-4-4
jan and walter take a look at this code this is giving me correct answers except for negative elements array
function [summa, index]=max_sum(b,n)
y=length(b)
q=movsum(b,n)
[maxsum,maxidx]=max(q)
summa=maxsum
index=(maxidx-floor(n/2))
if n==y
j=1
end
end
command window
max_sum([ 79 15 -18 -28 -30 52 -81 31 -74 4 57 -96],4)
y =
12
maxsum=
94 76 48 -61 -24 -87 -28 -72 -120 18 -109 -35
summa =
94
index =
1
index =
1
but i think my code is giving the right value plz take a look and tell me what to do
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Vikas Kumar
Vikas Kumar 2019-6-11
function [summa, index] = max_sum(A,n)
if length(A)<n
summa = 0;
index = -1;
else
B = maxk(A,n)
summa = sum(B);
z = zeros(1,length(B));
m = [];
for i = 1:length(B)
z = find(A==B(i));
m = [m z]
end
T = sort(m)
index = T(1,1)
end
end
Jaimin Motavar
Jaimin Motavar 2019-6-29
function [summa,index]=max_sum(a,b)
n=length(a);
summa=0;
total=0;
if b>n
summa=0;
index=-1;
return
end
for i=1:(n-b+1)
for j=i:(b-1+i)
total=total+a(1,j);
end
if total>summa
summa=total;
index=i;
end
total=0;
end
end
  2 个评论
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Roshan Singh
Roshan Singh 2019-9-15
function [summa, index]=max_sum(v,n)
L=length(v);
p=L-(n-1);
k=0;
t=0;
for i=1:p
z=n+k;
k=k+1;
s=0;
for d=i:z
s=s+v(d);
end
t(i)=s;
end
if (n<=L)
[summa index]=max(t);
else
summa=0;
index=-1;
end
end
Hussain Bhavnagarwala
function [summa,index] = max_sum(v,n)
if n>length(v)
summa = 0;
index = -1;
return
end
x = (length(v) - n) + 1;
tot =[];
t=0;
total = 0;
for k = 1:x
for i =1:n
total = total + v(t+i);
end
tot(k) = total;
t=t+1;
total = 0;
end
summa = max(tot);
ind= find(tot==max(tot));
index = ind(1);
end
Shashidhar Rai
Shashidhar Rai 2020-3-15
编辑：Walter Roberson 2020-3-15
I have written the code but it's showing error. Can anyone tell me what's wrong in it.
function [summa, index] = max_sum(v, m)
ii=1;
if length(v)
index=-1;
summa=0;
elseif length(v) ==n
index=1;
summa=sum(v);
else
summa=0;
start=1;
for ii =start : start +n-1
if summa < sum (v [start : start+n-1] )
summa=sum(v[ start : start +n-1] ) ;
index = start;
end
start =start +1;
if start
length(v) - n+1
break;
end
end
end
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Guillaume
Guillaume 2020-3-15
To add to the problem Walter pointed out:
  • the function has an input m that is never used, but use the undefined variable n instead.
  • there's a ii loop that never uses ii.
  • that loops will only ever do one iteration because the if start is always going to be true and break out of it.
Irfan Hussain
Irfan Hussain 2020-3-31
function [summa, index] = max_sum(v,n)
leng = length(v);
if leng < n
summa = 0;
index = -1;
else
w = [];
summa = 0;
for i = 1:leng
if summa < sum(v(i:n));
summa = sum(v(i:n));
index = i;
% x = sum(v(i:n));
%w = [w ,x];
if n < leng
n = n + 1;
%else
% summa = max(w);
% index = find(x == );
% end
end
end
end
end
  1 个评论
Shubham Pandey
Shubham Pandey 2020-4-3
this code has some error, wont work correctly for this case:
[summa index]=max_sum([ 45 -32 -25 27 78 -9 32 -1 -85 2 -32 -81 -32 -14 -31 46 -70 87 94 ], 15)
Jaimin Patel
Jaimin Patel 2020-4-7
function [X,Y] = max_sum(v,n) % X and Y are output arguments
X = -inf; %take -inf value of X for getting minus sum
p = n;
Y = 1;
if n > length(v)
X = 0;
Y = -1;
end
for i = 1:(length(v)-(n-1))
a = sum(v(i:p));
p = p + 1;
if a > X %condition for taking maximum sum of consecutive elements of vector
X = a;
Y = i;
end
end
simple code for solution...
Emine Ertugrul
Emine Ertugrul 2020-4-13
function [summa,index]=max_sum(v,n)
m=length(v);
if n>m
summa=0;
index=-1;
else
M = movsum(v,n,'Endpoints', 'discard')
[a,b]=max(M)
summa = a
index = b
end
end
  1 个评论
Walter Roberson
Walter Roberson 2020-4-13
I think the point of the assignment was not to use movsum() or other similar library functions, and to write the algorithm in more basic MATLAB.
Garvit Kukreja
Garvit Kukreja 2020-4-14
I have written this code. Can anyone tell me what's wrong in it.
Error : Variable summa has an incorrect value. max_sum([ -91 -57 -45 -8 -21 8 75 -80 89 -36 59 -71 -57 14 3 88 -79 -68 -6 ], 5) returned sum = 325 and index = 7 which is incorrect...
function [s,i]=max_sum(a,b)
B = maxk(a,b)
[n m]=size(B);
[y z] = size(a);
f=[]; %empty matrix
kk=0; %counter
if z>=b; %no. of element in 'a' more than or equal to'b'.
s=sum(B)
for ii=1:z;
for jj=1:m;
if B(jj)==a(ii);
kk=kk+1;
f(kk)=ii ;
end
end
end
i=min(f)
else
s=0
i= -1
end
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Garvit Kukreja
Garvit Kukreja 2020-4-14
编辑：Garvit Kukreja 2020-4-14
Thanks for your response.
it is sum of deduced matrix 'B',
where B=Maxk(a,b) ( If a is a vector, then maxk returns a vector containing the k largest elements of a)
program worked for this command : [summa, index] = max_sum([1 2 3 4 5 4 3 2 1],3)
Ahmed J. Abougarair
function [summa, index]=max_sum(v,n)
L=length(v);
p=L-(n-1);
k=0;
t=0;
for i=1:p
z=n+k;
k=k+1;
s=0;
for d=i:z
s=s+v(d);
end
t(i)=s;
end
if (n<=L)
[summa index]=max(t);
else
summa=0;
index=-1;
end
end
Ahmed J. Abougarair
function [summa, index] = max_sum(v,n)
k =length(v);
if k==n
summa = sum(sum(v));
index =1;
return
elseif k<n
summa = 0;
index =-1;
return
else
z = length(v);
summa = 0;
index = -1;
if n <= z
for i = 1:(z - n + 1)
total = sum(v(i:n - 1 + i));
if total > summa
summa = total;
index = i;
end
end
end
end
Roshan Barnwal
Roshan Barnwal 2020-4-27
function [summa, index] = maxsum(v,n)
summa = sum(v(1:n-1));
for j = 2:length(v) -2;
r = sum(v(j:j+n-1));
if summa<r
summa=r;
index = j;
end
end
%% this works well but in few cases it asks for some error. can any one help me to short out the problem?
Salman P H
Salman P H 2020-4-30
function [summa,index] = max_sum(v,n)
if n>length(v)
summa = 0;
index = -1;
return;
end
x=1;
y=n;
great = -inf;
while y<=(length(v))
z = sum(v(1,x:y));
if z>great
great=z;
a=x;
x=x+1;
y=y+1;
elseif great==z
a=x-(x-a);
x=x+1;
y=y+1;
else
x=x+1;
y=y+1;
end
end
summa = great;
index = a;
end
Olel Arem
Olel Arem 2020-4-30
function [summa,index]=max_sum(v,n)
len_v=length(v);summa=0;poss=[];ii=1;jj=n;
if n>len_v
summa=0;
index=-1;
return
end
while jj<=len_v
poss(ii)= sum(v(ii:jj));
[summa,index]=max(poss);
ii=ii+1;
jj=jj+1;
end
Prithvi Shams
Prithvi Shams 2020-5-5
Here's my version of the code.
While the problem can be solved with movsum() in a single line, it's recommended to utilize if and for loops as a learning exercise.
function [summa, index] = max_sum(v, n)
if n > numel(v)
summa = 0;
index = -1;
else
j = n;
for i = 1:(numel(v) - n + 1)
s(i) = [sum(v(i:j))];
j = j + 1;
end
if numel(max(s)) > 1
m = max(s);
[summa index] = m(1);
else
[summa index] = max(s);
end
end
anuj chaudhari
anuj chaudhari 2020-5-5
编辑：anuj chaudhari 2020-5-5
function [a, b] = max_sum(v,n)
if ~isscalar(n)||n<0||n~=fix(n)
error('n must be a positive integer')
end
[~,c]=size(v);
d=length(v);
r = zeros(1,d-n+1);
if n>c
b=-1;
a=0;
else
for k=1:(d-n+1) %from here, this is a means of movsum
r(k)=sum(v(k:k+n-1));
[a, b]=max(r);
end
end
end
Shandilya Kiran Bhatt
You can also solve this question by using while loop if you don't know movsum function like me.Look at following code:-
function [summa , index ] = max_sum(A,n)
b = length(A);
c = zeros(1,b-n+1);
i = 1;
if b < n
summa = 0;
index = -1;
else
while n<=b && i<=b
c(1,i) = sum(A(i:n));
n = n+1;
i = i+1;
end
[summa , index ] = max(c);
end
Tahsin Oishee
Tahsin Oishee 2020-5-17
function [summa,index]=max_sum(v,n)
summa=0;
index=0;
w=1;
[b a]=size(v);
if n>a
index=-1
summa=0;
else
if n<=a
for i=1:(a+1-n)
sum=0;
for j=1:n
sum=sum+v(w);
w=w+1;
end
w=w-n+1;
if sum>summa;
summa=sum;
index=v(i);
end
summa
index
end
end
end
end
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Walter Roberson
Walter Roberson 2020-5-17
You already have two loop control variables, i and j: use 2D indexing instead of doing strange things with w.
We recommend against naming a variable sum: it is very common to want to use the sum() function after having used sum as a variable.
khyathi beeram
khyathi beeram 2020-5-18
编辑：khyathi beeram 2020-5-18
function [summa index]=max_sum(v,n)
a=[ ];
if n<=length(v)
for i=1:length(v)-(n-1)
sum=0;
for j=i:i+n-1
sum=sum+v(j);
end
a(i)=sum;
end
summa=max(a);
g=find(a==summa);
index=g(1,1);
else
summa=0;
index=-1;
end
end
vighnesh rana
vighnesh rana 2020-5-19
function [summa,index] = max_sum(A,n)
if length(A)< n
summa = 0;
index = -1;
return;
end
summa = -inf;
index = -1;
for i = 1:(length(A)-n+1)
total = sum(A(i:(i+n-1)));
if total > summa
summa = total;
index = i;
end
end
end
Taif Ahmed BIpul
Taif Ahmed BIpul 2020-5-20
function[summa,index]=max_sum(v,n)
if size(v,2)<n
summa=0;
index=-1;
return
end
p=size(v,2)-(n-1);
k=1;
A=zeros(1,n);
summ1=zeros(1,p);
for i=1:p
jj=i;
while jj<=(i+n-1)
while k<=n
A(k)=v(jj);
jj=jj+1;
k=k+1;
end
end
summ1(i)=sum(A);
k=1;
end
summa=max(summ1);
index1=find(summ1==max(summ1));
if size(index1,2)>1
index=index1(1);
return
else
index=index1;
end
utkarsh singh
utkarsh singh 2020-5-21
function [summa, index]=max_sum(m,n)
if numel(m)<n
summa=0;
index=-1;
else
summa=-inf;
for i=1:(numel(m)-n+1)
j=m(i:i+n-1);
maxsumma=sum(j);
if(maxsumma>summa)
summa=maxsumma;
index=i;
end
end
end
end
sai teja
sai teja 2020-5-28
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
Kumar Shubham
Kumar Shubham 2020-6-2
编辑：Kumar Shubham 2020-6-2
function [summa, index]= max_sum(v,n)
if n > length(v)
summa = 0;
index = -1;
return;
elseif n<=length(v)
a=movsum(v,[0,n-1]);
b=a(1:length(v)-n+1);
[summa,index]= max(b);
end
end
Sumit Kumar Sharma
function [summa, index]=max_sum(v,n)
l=length(v);
if n>l
summa=0;
index=-1;
else
p=l-n+1;
ii=0;
total=-inf;
for j=1:p
s=sum(v(j:n+ii));
ii=ii+1;
if s>total
total=s;
index=j;
else
continue;
end
end
summa=total;
end
end
KAVITI BHARGAV RAM NAIDU
编辑：KAVITI BHARGAV RAM NAIDU 2020-6-5
function [summa,index] = max_sum(v,n)
b=zeros(1,length(v)-n+1); % initializing the b vector(only zeros) of length = length(v)-n+1
% this will decrease time taken for getting answer
if n > (length(v)) % if n is larger than length of v sum = 0 and index = -1 as per question (last line)
summa = 0 ;
index = -1;
else
for p = 1:[length(v)-n+1]
b(1,p) = sum (v(p:p+n-1)); % b(1,1)= v(1,1)+v(1,2) (if n = 2)
end % giving values to vector b using sum function
[summa index] = max(b); % if n = 2 sum should be between 2 consecutive elements.
end % if p = 2 and n = 2 sum between 2 nd and 3rd element should be considered
% p+n-1 = 2+2-1 = 3 // sum (v(2:3)) means sum of 2nd and 3rd element of vector b.
% so sum(v(p:p+n-1))
Methil Muley
Methil Muley 2020-6-4
zineb britel
zineb britel 2020-6-4
%what's wrong with my code
function [summa index]=max_sum(v,n)
index=0; summa=0;
if n > length(v)
summa= 0;
index=-1;
else
a=sort(v,'descend');
summa= sum(a(1:n));
index_row= find(v>=a(n));
index= min(index_row);
end
end
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Ujjawal Barnwal
Ujjawal Barnwal 2020-6-8
function [summa , index]=max_sum(v,n)
summa=sum(v(v<0));
for ii=1:(length(v)-(n-1))
t=0;
for jj=ii:(ii+(n-1))
t=t+v(jj);
end
if (t>summa)
summa=t;
index=ii;
end
end
end
AYUSH MISHRA
AYUSH MISHRA 2020-6-13
编辑：AYUSH MISHRA 2020-6-13
function [summa, index] = max_sum(v,n)
if n > length(v)
summa = 0;
index = -1;
return;
end
summa = -inf;
index = -1;
for ii = 1:length(v)-n+1
currentV = v(ii:(ii+n-1));
currentSumma = sum(currentV);
if currentSumma > summa
summa = currentSumma;
index = ii;
end
end
end
Maddireddy Harshavardhan Reddy
Create a row vector named x that starts at 1, ends at 10, and contains 5 elements.
Sneha Paul
Sneha Paul 2020-6-19
function [summa,index]=max_sum(v,n)
z=[];
if n>length(v)
summa=0;
index=-1;
return
elseif (n<=length(v))
for i=1:length(v)-(n-1)
z(i)=sum(v(i:i+(n-1)));
end
end
[summa,index]=max(z)
MICHAEL
MICHAEL 2020-6-19
function [s,i] = max_sum(v,n)
s = 0; i = 0;
len = length(v);
l = len-n+1;
if n>len
s = 0;
i = -1;
else
for j=1:l
if j==1
s = sum(v(j:n));
i=1;
end
if s<sum(v(j:n))
s = sum(v(j:n));
i = j;
end
if n<len
n=n+1;
end
end
end
end
Sakib Javed
Sakib Javed 2020-6-22
编辑：Sakib Javed 2020-6-22
ffunction [summa index] = max_sum(A,n)
m=length(A);
if n > m
summa = 0;
index = -1;
return;
end
B = [];
q=m-(n-1);
for ii = 1:q
B=[B sum(A(ii:ii+n-1))];
end
[summa index] = max(B);
end

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