# Formula for a curve

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Would someone help me determine the formular for a curve that plots to these values:If Miles = 0, then Offset = 5;If Miles = 10, then Offset = 500;If Miles = 20, then Offset =2000.I would like to have a formula that would calculate the Offset for any known value of Miles between 0 and 20 and would be xml friendly.Thanks,Glenn

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Hi,(Long tima ago??????????????????????)Looks like something as a parabole:y = ax2 + b Jan"Beatus ille qui procul negotiis..."

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>Would someone help me determine the formular for a curve that>plots to these values:>If Miles = 0, then Offset = 5;>If Miles = 10, then Offset = 500;>If Miles = 20, then Offset =2000.>I would like to have a formula that would calculate the Offset>for any known value of Miles between 0 and 20 and would be xml>friendly.>Thanks,>Glenn>What you're wanting to do is called forecasting in statistics.It's not really complex... but it would be in XML. I don't do XML... but I do C... here's a C version... maybe you can translate it?FLOAT64 Offset_By_Miles(FLOAT64 miles_index){ FLOAT64 Miles[3] = {0,10,20}; FLOAT64 Offset[3] = {5,500,2000}; int i; FLOAT64 sx, sy, xmean, ymean, sxx, sxy, syy, x, y; FLOAT64 B0, B1; //{compute basic sums} sx = 0.0; sy = 0.0; sxx = 0.0; sxy = 0.0; syy = 0.0; for (i = 0; i < 3; i++) { x = Miles; y = Offset; sx = sx+x; sy = sy+y; sxx = sxx+x*x; syy = syy+y*y; sxy = sxy+x*y; } xmean = sx/(float)3; <<- number of items ymean = sy/(float)3; sxx = sxx-(float)3*xmean*xmean; syy = syy-(float)3*ymean*ymean; sxy = sxy-(float)3*xmean*ymean; //{check for zero variance} if (sxx <= 0.0) { // bad return 0; } B1 = sxy/sxx; B0 = ymean-B1*xmean; // forecast Y based on X; return B0+B1*miles_index; //2049.75}

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Glenn,(miles) sp0l0 sqr 5.025 * l0 0.75 * - 5 + (>Offset)2nd order polinomial, R2=1Hope this helps.Tom

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Hi,Tom was first!Old dutch mathematics for parabole:y (offset) = ax2 + bx + cYour data 0-5; 10-500; 20-2000So c = 5and after some calc a = 5.025 and b = -0.75That gives y = 5.025 * Miles2 - 0.75 * miles + 5 in xml:(L:Miles,number) (L:Miles,number) * 5.025 * (L:Miles,number) 0.75 * - 5 + (>L:Offset,number) "Mustard after meal"Jan"Beatus ille qui procul negotiis..."

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""and after some calc""Not too much calcs indeed, aprox. 30 secs to find the formula in Excel. :-)Tom

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Great, thanks, guys. I'll put these to the test over the weekend.Glenn

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Yeah Tom got in before me, but if you plot curves in Excel it can tell you the formula, especially if it has a regular mathematical shape.cheers,nick

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My daughter has been praising Excel for years. They gave me MS Office for Christmas because my old Word 97 was coughing up blood if graphics got a bit heavy. I've never run anything in the Office suite other than Word. I always thought Excel was just a spreadsheet for business applications such as taxes, etc. I'll definitely look into it now. Thanks for the tip.Glenn

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