Description:
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I checked the bug reports and did not see this as an issue, so hopefully no one will get too mad at me for posting this...I'm a virgin to bug reporting :).

When using the Spreadsheet_Excel_Writer package for PEAR, formulas must be written in capital letters.  In other words, you can not write "=SUM(a1:a10)".  It must be written as "=SUM(A1:A10)".

A simple fix for this is the following:

Edit the writeFormula() function to include

$formula = strtoupper($formula);

as the first line of the function.

I don't know if this is the best way to fix the problem, but this is my first bug report/patch, so it looks good to me :).

Reproduce code:
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<?php
require_once 'Spreadsheet/Excel/Writer.php';

// We give the path to our file here
$workbook = new Spreadsheet_Excel_Writer('C:\\bugs\\bug.xls');

$worksheet =& $workbook->addWorksheet('My first worksheet');

$worksheet->write(0, 0, 1);
$worksheet->write(1, 0, 2);
$worksheet->write(2, 0, 3);

// Formula must be in upper case.  This line will not work.
$worksheet->write(3, 0, "=SUM(a1:a3)");

// We still need to explicitly close the workbook
$workbook->close();
?>

Expected result:
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Apache.exe - Application Error

The exception unknown software exception (0xc00000fd) occurred in the application at location 0x0084823d.

Click on OK to terminate the program
Click on CANCEL to debug the program