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Making your own trenlines
Since I'm working databases that are subject to change, I would like to be
able to make my own trendline formulas. The built-in trendline function of excel doesn't let me use the trendline formula shown in the graph, and I don't want to manually change my formulas each time my database changes. I've been able to make my own linear- and 'power'trendlines as follows: My linear trendline: form: y=a*x+b a=SLOPE(Yrange;Xrange) b=INTERCEPT(Yrange;Xrange) Mijn 'Power'trendline: form: y=a*x^b a=EXP(INTERCEPT(LN(Yrange);LN(Xrange))) b=SLOPE(LN(Yrange);LN(Xrange)) So currently I'm looking for the following two: Logarithmic trendline in the form: y=a*Ln(x)+b Exponential trendline in the form: y=a*e^(b*x) Thanks in advance, Maarten |
#3
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Thanks a lot for your help.. I guess I haven't been drinking enough coffee
today ;) "Tushar Mehta" schreef: I'm surprised you figured out the first two and then got stumped by the last two. y=a*ln(x)+b is of the same form as y=a*z+b! So, a=Slope(y,ln(x)), and b=intercept(y,ln(x)) The other equation, y=a*exp(b*x), can be rewritten as ln(y)=ln(a) + ln(exp(b*x)) or ln(y)=ln(a) + b*x So, a=exp(intercept(ln(y),x)) and b=slope(ln(y),x) -- Regards, Tushar Mehta www.tushar-mehta.com Excel, PowerPoint, and VBA add-ins, tutorials Custom MS Office productivity solutions |
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