inquiry about a command

im trying to answer this question

Write a program to calculate: X = 1/a – 1/2a + 1/3a – 1/4a + ………… – 1/100a For values of a = -5, -3, -1, 1, 3, …50

so far ive tried

a=[-5:2:50];

>>  n=[1:100];

>>  x=0;

>> for i=1:100

term= (-1.^n +1)/a*n;

x=x+term;

end

but i keeps giving me error (Error using /)

the next question is

Without using loops, generate the vector x = [1 1/2 1/3 1/4 1/5 1/6 … 1/100].

and ive tried putting

n=[2:99]

x=[1/1 :1/n :1/100]

is that right

thx

Answer 1

[Walter Roberson]

See the ./ (rdivide) operator and the .* (times) operator

[mohamed]

what about it

[Walter Roberson]

You used the / operator. That is the wrong operator for your purpose. Use ./ instead.

Answer 2

[Andrei Bobrov]

a=-5:2:50;
n=1:100;

X = -sum((-1).^n./n)*a; % EDIT

[Andrei Bobrov]

corrected