Ivan
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| posted on 13/10/09 at 02:46 PM |
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OT Maths question
Help - I've even forgotten if I knew this 40 years ago when studying maths  as it's completely Greek to me now.
Just did a 3rd order polynomial curve fit in Excel and got the following equation
y = 13.224x^3 - 79555x^2 + 2E+08x - 1E+11
Now want to calculate some y values but don't know what the "E" is and what it's value is.
There's obviously more to it than meets the eye as +2E-1E = E but they kept them separate, and what's the implication of "08x"
- why not just "8x"?????
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cd.thomson
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| posted on 13/10/09 at 02:53 PM |
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E = times ten to the power of
so:
y = 13.224x(to the power of) 3 - 79555x(to the power of) 2 + 2 x 10(to the power of)8x - 1 x 10(to the power of)11
[Edited on 13/10/09 by cd.thomson]
Craig
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nick205
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| posted on 13/10/09 at 02:54 PM |
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badda, badda, what...?
Doesn't the "E" mean to the power of like on a calculator?
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omega0684
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| posted on 13/10/09 at 02:58 PM |
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E means Exponential e.g 218400000 = 2.184E08
[Edited on 13/10/09 by omega0684]
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kennyrayandersen
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| posted on 13/10/09 at 03:06 PM |
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quote:
Originally posted by nick205
badda, badda, what...?
Doesn't the "E" mean to the power of like on a calculator?
I think you are right and omega0684 has laid it out there -- least that's the way us en-gan-eers talk
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rallyingden
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| posted on 13/10/09 at 03:18 PM |
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Ivan
Just change your cells within excel to "number" format and you will see the number displayed in full.
Excel uses E to allow large numbers to be displayed in small cells. Omega0684 is correct
RD 
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scootz
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| posted on 13/10/09 at 03:20 PM |
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quote:
Originally posted by Ivan
Just did a 3rd order polynomial curve fit in Excel and got the following equation
y = 13.224x^3 - 79555x^2 + 2E+08x - 1E+11
Now want to calculate some y values but don't know what the "E" is and what it's value is.
I can't remember my 7-times table let alone the gobbledy-gook you're plotting with!
I don't even use a calculator these days - I just ask on here if I have a hard sum to do!
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Alex.
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| posted on 13/10/09 at 03:24 PM |
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quote:
Originally posted by omega0684
E means Exponential e.g 218400000 = 2.184E08
[Edited on 13/10/09 by omega0684]
That would be 'e', in lowercase.
Alex.
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omega0684
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| posted on 13/10/09 at 03:40 PM |
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quote:
Originally posted by Alex.
quote:
Originally posted by omega0684
E means Exponential e.g 218400000 = 2.184E08
[Edited on 13/10/09 by omega0684]
That would be 'e', in lowercase.
Alex.
depends if your writing with caps lock on
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liam.mccaffrey
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| posted on 13/10/09 at 04:22 PM |
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lower case e would be the mathematical irrational constant
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MikeRJ
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| posted on 13/10/09 at 05:01 PM |
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Be careful if you are using the polynomial from an Excel curve fit to actual generate your own data, you may find the generated data has very large
errors.
The problem is the number decimal places that Excel displays by default can be much lower than required. If you right click on the box in your chart
displaying the polynomial, select "Format data labels" and choose the "Number" tab, you can now select "Number" as
the Category and select the number of decimal places to display. You often need a lot of digits to get good data from higher order polynomials.
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Ivan
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| posted on 13/10/09 at 07:42 PM |
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Thanks guys - tomorrow when I am more alert I will try out your suggestions.
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Alex.
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| posted on 14/10/09 at 07:43 AM |
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quote:
Originally posted by liam.mccaffrey
lower case e would be the mathematical irrational constant
It would also be the inverse of a natural logorithm (ln). Which would make more sense in the original equation than the mathematical irrational
constant.
Both of which are not the answer to the original question! 
Alex.
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Ivan
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| posted on 14/10/09 at 09:11 AM |
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After thinking about it for a while the normal expression for this type of curve is "y= Ax^3 - Bx^2 + Cx - D" so I would guess that the
equation is most probably "y = 13.224x^3 - 79555x^2 + (2E+08x) - (1E+11)"
Unfortunately that and just about any other combination gives absolutely ridiculous answers in the order of Billions instead of hundreds
For instance where x=2003, y should approx 400 but calculates to 87 700 000 000
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alistairolsen
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| posted on 14/10/09 at 09:43 AM |
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y = 13.224x^3 - 79555x^2 + 200000000x - 100000000000
so for X= 2003
Y= 13.224(8036054027)-79555(4012009)+400600000000-100000000000
=106268778453.05-319175375995.00+400600000000.00-100000000000.00
=87693402458.05
Sorry for the horrendous notation but it avoids any potential confusion.
How did you find the equation?
My Build Thread
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Ivan
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| posted on 14/10/09 at 09:57 AM |
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quote:
Originally posted by alistairolsen
How did you find the equation?
Calculated it using Excel's charting trendline fascility.
I am rethinking using lower values of x which is the year i.e. 1 for 1999 and 10 for 2009 and higher values for vehicles i.e. 389 000 instead of 389
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