I would like to accomplish in PHP something that easily done in Excel.
I have an array of data, I would like to calculate the Logarithmic trenline in order to graph it late ron.
I have found out that the equation of a logarithmic trendline is calculated in Excel using the following formulat:
Equation: y = (c * LN(x)) - b
c: =INDEX(LINEST(y,LN(x)),1)
b: =INDEX(LINEST(y,LN(x)),1,2
How can I calculate b and c in PHP? I have not been able to find an equivalent of the INDEX and LINEAR function that is available in Excel.
Can ayone help me with that?
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You can fit a trend line of the form y = (c * LN(x)) - b
to a set of (x,y) points by keeping track of
count
array_sum($y);
$LN=array_map("log",$x);
array_sum($LN);
array_sum(array_map("multi
array_sum(array_map("multi
array_sum(array_map("multi
function multiply($n, $m)
{
return($n * $m);
}
see
http://mathworld.wolfram.c
Ozo,
I tried using the info you gave me and the page:
http://mathworld.wolfram.c
But I can't get the equation right, would you be able to tell me what I've done wrong?
Here's what I have come with:
$b = ( (count($y) * array_sum(array_map("multi
( ( count($y) * array_sum(array_map("multi
$a = ((array_sum($y) - count($y) * $b) * array_sum($LN)) / count($y);
But it doesn't work...
Business Accounts
Answer for Membership
by: virmaiorPosted on 2007-02-20 at 12:30:59ID: 18573676
if you could tell me what the functions INDEX and LINEST do then it might be easier to answer your question. As those are rather ambiguous from a linguistic perspective and I have not dabbled in Excel for a while.