So, we can use 2, 1. You'll also want to do this coming the other way, so we can use 0, 0. Now enter the formula to calculate the y-value. Now click on the box that you just entered the formula into, then drag from the bottom-right of that box down to the final x-value to insert the formula into each one—you'll notice the y-values pop up. Now in the third column, let's enter the formula to calculate the secant slope. Just as before, drag down from the bottom-right to apply the formula for the rest of the x- and y-values.
Now just rinse-and-repeat, using x-values going the other way. Apply the same drag technique for these. For a further detail, check out the video below. Get the Gadget Hacks Daily Life hacks for your smartphone. Sign Up.
- LINEST Extended.
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Share Your Thoughts Click to share your thoughts. In addition to showing how to apply LINEST for a polynomial, the article also shows how to apply it for other data fits including logarithmic, powers, and exponentials. HH represents the known y values; in my case, these were C V data points I read for different disc angles from the Bray valve data sheet.
GG represents the x values corresponding to the y values you know. If you want the other statistics or to force the intercept to be 0, you would use a form of the function that looks like this:. As far as the new parameters go:. If you omit this parameter, the intercept is not forced.
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If you omit this parameter, they are not returned. But, for my aging brain at least, the Excel tutorial did not include an example of how to do what I wanted to do at least not one that I understood. So, I am very grateful to whom-ever it was that wrote the article I mentioned previously. Array formulas are powerful Excel tools that allow you to summarize data in many different ways. But for the current discussion, I found it easier to think of them as formulas that work with a range of numbers as inputs that also return answers that are more than one number, thus needing an array of cells more than one for their output.
To create an array formula, you type the formula into a cell, which becomes the upper left corner of the range you want to have your output show up in. That actually sounds more complicated than it is. The bottom line is that the LINEST function needs an output range that is at least one row high with a column for each coefficient in the polynomial along with the y intercept.
If you want the additional statistics, then you need 5 rows instead of 1 row in addition to including those parameters in the LINEST formula. In my case, I was only looking for the coefficients for the polynomial. Note that the labels m 5 , m 4 , m 3 , m 2 , m 1 , and b were ones that I placed in advance for my own reference; if nothing else, it helps me see which cells to select for the next step. You can also see that it references the disc angle data for the second parameter the green box and green text in the formula.
But each cell yields a different result, with the results being the parameters of interest. In this screen shot above, the cell highlighted in green is where I originally entered the formula. But those seemingly insignificant digits make a big difference in the results you get if you use them to assess the polynomial. I guess all of this comes back to something that my teachers and mentors have taught me ever since I started adding 1 plus 1 to get 2.
That being that its always good to check your answer somehow before moving forward with it. In this case, when I took the step of plotting the results of the equation I had developed from the trend line coefficients, I discovered there was a problem. Another trick you can use with the functions generated by the trendline function within a graph is to right click on the trendline label, click format trendline label, then change the format category to number and increase the decimal places to however many are appropriate.
That method can be a little more expedient depending on the situation and level of precision called for. Thanks much for sharing Ben. That would be much faster than the approach I used. A couple of guys that I work with offered a few comments in a discussion I was having with them about this.
MS Excel: How to use the LINEST Function (WS)
One is an amusing quote forwarded by Steve Briggs;. John von Neumann via Wikiquote. The latter is probably the real reason I did the post. Its pretty easy to see stuff in a spreadsheet and just figure its right and off you run with it. That takes a little time, but is usually worth it, even if all it does is give you the comfort of the assurance that you are on the right track. Another way to do it is to use one of the orthogonal basis functions one of a family which are all solutions of singular Sturm-Liouville Partial Differential Equations PDE.
I use these mostly Legendre and Chebyshev to solve PDEs, which has different math behind it than doing curve fits. I found this link:. The basic format is the same:. These can be written as cosine functions with a change of variable, or as adapted polynomials. This then gives you an equation you can use. Another tidbit: At their very core, most transcendental functions like trig functions, etc can be represented using exponentials. I will be sure to mention you in my Thesis. Fantastic article on this function. Explained in better detail than the Excel Help section.
This has turned out to be one of my most popular posts and on occasion, I have wondered if it was actually useful or if it was so far off the mark that there were a bunch of mathemeticians passing it around as the joke of the day. So, its good to hear that it was helpful. So I too had the same issue with excels formulae. Interestingly you can format the formula on the chart in the same way you format the data in a cell. I formatted the formuala to scientific numbering with 6 decimal places and low and behold the plotted data wa perfect. This is by an order of magnitude, my most popular post, which is odd given that the blog is basically about HVAC.
For a while, I thought it probably was being passed around by really smart people in Math departments as the joke of the day. But it seems others, like you and I, have been puzzled by the same thing. So I learned two things, one being the stuff in the post and the other being the formatting trick. Always something to learn with Excel.
Thanks for your feedback and for visiting the blog. If you look at the m1 coefficient, there is a symbol mistake. The two values differ by a factor of And then this might make a huge difference in your conclusion that the number of significant numbers or digits after the decimal place makes a large difference. Sharp eyes; out of the 43, people who have looked at that post it is by far, my most popular post, even more popular than the ones about how to make a Jeopardy game , you are the first one to notice the typo, or at least the first one to say something.
Thanks much. I have fixed the graphic and the reality is that it was a typo in my transcription of the equation coefficients. Meaning Excel was actually working with the negative number.
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And while I agree that if Excel had been working with the positive number, it would have made a difference, the conclusion I reached about the decimal places mattering is still valid. In other words, the conclusion and math was based on the negative number, not the typo.
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And the number of decimal places you use when you generate the multi-order polynomial can have a huge impact on the result as will getting the sign wrong if you are not careful when you type things in. The procedure is very similar to what I show in the blog post. I do that a lot myself.
There are lots of tips and tricks you can do with Excel to curve-fit any given data set, but no matter how perfect you can fit the curve, prediction out side the range of your actual hard data is always risky. It all comes down to how confident you are with your work, and if it was to be scrutinized how well you can defend yourself.
Best way to play safe is to stay within the range of your hard data — that is only do interpolations, never extrapolations. This way you can have it retrieve a single y value using the trendline values based on a given x value in a single cell, and update the y value if the x changes. Great information. Really informative and so much better than the default Excel Help files.
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