How do you change curve fitting equation formats?

**PhilHenshaw** · 10-06-2009, 09:53 AM

In the formulas for curves fitted to the data on a graph I can no longer figure out what the exponential equation syntax is. It seems they're omitting the real number portion of the exponent... Am I nuts? Can anyone help me find where the real formula is hidden?

like: the Excel generated formula “y = 62.51e^5E-05x” … I don't see what the exponent 5E-05x means

**shg** · 10-06-2009, 10:19 AM

Welcome to the forum.

It means 0.00005.

A formula that calculated the same result (withing the precsion shown) is = 62.51 * exp(5E-05 * x)

**PhilHenshaw** · 10-06-2009, 10:41 AM

Yea, that's what it looked like. That an exponent of a natural growth process has only one significant digit is the problem. Where did they hide all the other significant digits?

**shg** · 10-06-2009, 10:44 AM

You can select the formula, and increase the number of significant digits, just as if it were a cell.

Our use LINEST to compute them on the worksheet.

**PhilHenshaw** · 10-06-2009, 12:55 PM

Thanks, I had actually right clicked on the formula, more than once..., and so couldn't find it before.

LINEST and LOGEST don't seem to return a linear or log fit to the data, or else I'm using it wrong. I inputed the lists of y & x data values in the first two places of the functions, with two commas to follow, and got an #value error. Is there a function that lets me output the y values of a plotted fit curve to the worksheet?

**shg** · 10-06-2009, 01:00 PM

For an exponential fit y = m * exp(LNb * x) = exp(LNm + LNb * x), select two horizontally adjacent cells and array-enter =LINEST(LN(y), x)

Then LNb is in the cell on the left, and LNm is in the cell on the right.

Please edit your thread title to describe your problem.