OpenEuphoria

2. Re: Unusually clear pseudocode example

• Posted by Jason Gade <jaygade at yahoo.com> Oct 25, 2005
• 493 views

DB James wrote:
> 
> 
> Hi,
> 
> Found this on the web while searching on "pseudocode" -- it seems like a good
> clear example of a presention of an algorithm.  A collection of such
> algorithms,
> done consistently in form, would be valuable.  As it is, the pseudocode on the
> web seems a mish-mash that ranges widely in value.  Even this example is
> mildly
> biased toward C++.  Ideally there would be no program bias.  I did use this
> in writing a slope and intercept function.
> 
> ------------------------------------------------------------------
> from:
> <a
> href="http://www.mines.edu/Academic/courses/math_cs/macs261/LABS/F00/lab7.html">http://www.mines.edu/Academic/courses/math_cs/macs261/LABS/F00/lab7.html</a>
> 
> LEAST SQUARES LINE
> 
> PURPOSE: Find the equation of the least squares line for a set of n data
> points (x,y).  Slope is its slope, and YIntercept it its y intercept.
> SumX, SumY, SumX2, and SumXY are the sums of the x's, the y's, the squares of
> 
> the x's, and the products x*y.  XMean and YMean are the means of the x's
> and the y's, respectively 
> 
> INPUT:   A collection of data points (x,y)
> 
> OUTPUT:  The equation of the least squares line
> 
> 
> ALGORITHM:
> 
> Step 1   Initialize n, SumX, SumY, SumX2, SumXY all to 0.
> 
> Step 2   Read the x-coordinate of the first data point x.
> 
> Step 3  While the end of data has not been encountered, do the following
>         
> 	Step 4  Read the y-coordinate of the data point, y. 
> 
> 	Step 5  Increment n by 1.
> 
> 	Step 6  Add x to SumX
> 
>         Step 7  Add x^2 to SumX2
> 
>         Step 8  Add y to SumY
> 
>         Step 9  Add x*y to SumXY
> 
>         Step 10 Read the next data point x,y
>         
>         End while 
> 
> 
> Step 11 If n > 0 then call CalculateSlopeIntercept
>         and display least squares line
> 
> Step 12 Else Display a message that no data points were read.
>         
>         End If/Else
> 
> End Main
> 
> PROCEDURE: CalculateSlopeIntercept
> 
> INPUT:  SumX, SumY, SumX2, SumXY, n
> 
> OUTPUT:  Slope of least squares line, and YIntercept of least 
>          squares line.
> 
> ALGORITHM:
> 
> Step1  calculate   XMean = SumX/n and YMean = SumY/n
>        
> Step2  calculate   Slope = (SumXY - SumX*YMean)/(SumX2 - SumX*XMean)
> 
> Step3  calculate   YIntercept = YMean - Slope * XMean
> 
> Step4  return  Slope and YIntercept
> 
> The algorithm assumes a main portion and a function call to a procedure called
> ComputeSlopeIntercept. In C++ this would be a main() function and a void
> function
> ComputeSlopeIntercept with 5 value parameters and 2 reference parameters. Step
> 4 in the procedure algorithm, return Slope and YIntercept is achieved through
> assignment of the reference parameters. No explicit return statement is
> needed.
> 
> The output of the program is bracketed by an if/else structure to avoid
> calling
> the procedure ComputeSlopeIntercept with no data points. The output should
> include
> the format of a line in slope-intercept form y = mx + b. This equation should
> be displayed on the screen. 
> ----------------------------------------------------------------------
> 
> --Quark

I haven't worked on it for awhile, but I wish that I had clear explanations like
this for the Great Computer Language Shootout code... it would make the task much
easier.

What I do now is translate from C or whatever other language is the most clear
but I still don't always understand what I'm doing. If I had clearer explanations
I would be able to see how to use Euphoria's strengths better.


j.