MATLAB: How to multiply simplest way this two vectors

matrixvectors

I have to multiply this xi and y this way:

xi = [98 99 100 101 102 103]; y = [2 4 6 4 3 1]; x = [ 98*ones(1,2), 99*ones(1,4), 100*ones(1,6), 101*ones(1,4),… 102*ones(1,3), 103*ones(1,1) ]

it is possible to somthing this to make…. x = xi.*( ones(1,y(1:end)) ) % this is not working

xi = [98 99 100 101 102 103];
y =  [2  4  6   4   3   1];
x=cell2mat(arrayfun(@(a,b) a*ones(1,b),xi,y,'un',0))

%or you can do it just by using a for loop

A simple and robust method:

>> str2double(num2cell(reshape(' 98 99 99100101102',3,[])',2))
ans =
    98
    99
    99
   100
   101
   102

Or less preferable (because it calls eval):

>> str2num(reshape(' 98 99 99100101102',3,[])')
ans =
    98
    99
    99
   100
   101
   102

And of course you can read the file data as strings:

>> C = textscan(' 98 99 99100101102','%3c','whitespace','');
>> C{1}
ans =
 98
 99
 99
100
101
102

and then use either of the methods as above to convert to numeric.

Read about sub2ind. This should be used for your case.

val = [98 99 100] ; 
idx = sub2ind(size(my_mat),x,y) ; 
my_mat(idx) = val ;