problem writing a seemingly easy summation

hi everyone I have this matrix P and for each column j I need to have a summation from second row to end, or i=2:end

for example

 P=[1 3 5 7;3 5 7 9;2 4 6 8];

now the matrix I am looking for is [5 9 13 17]

but no matter how I try to write it the answer is second row only

can someone help?

thank u in advance

Answer 1

[Adam]

sum( P(2:end,:) )

[alexaa1989]

it has to produce a (1,4) matrix not only a number in the example in need to produce [5 9 13 17] not sum of them

[Adam]

It should produce your 1 by 4 matrix.

To be more explicit you can use:

sum( P(2:end,:), 1 )

but that is the same as the default behaviour, or at least it is when I run it.

[alexaa1989]

it just gives 37

[Adam]

Can you paste in the whole Matlab commands with results output to command line? In the answer below you said it gave 34 so it sounds as though something odd is happening with your code or your Matlab.

I get exactly the same as Guillaume posted when I run this command.

sum (and most functions of that type) on a 2d matrix will, by default sum each column and give you a result which is 1-by-numColumns.

Answer 2

[Guillaume]

sum(P(2:end, :))

[alexaa1989]

it has to produce a (1,4) matrix not only a number in the example in need to produce [5 9 13 17] not sum of them

[Guillaume]

have you tried the command? It produces exactly what you asked for

>>P=[1 3 5 7;3 5 7 9;2 4 6 8];
>>sum(P(2:end, :))
ans =

     5     9    13    17

[alexaa1989]

yes I tried it produces 34 is my matlab not working correctly?

[alexaa1989]

it has this text when running

Warning: MATLAB Toolbox Path Cache is out of date and is not being used. Type 'help toolbox_path_cache' for more info

[Adam]

rehash toolboxcache

should fix that I think

[Guillaume]

Can you copy and paste EXACTLY what you wrote in matlab?

I doubt it has anything to do with the path cache (unless you've created your own sum function). Restart matlab to update the cache.

[alexaa1989]

is it possible that I have been using false data???!!!!

[alexaa1989]

how can i reset MATLAB for update?