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Re: [avr-gcc-list] update on the last issue


From: intiha Ho gai
Subject: Re: [avr-gcc-list] update on the last issue
Date: Tue, 5 Apr 2005 15:25:37 -0700

On Apr 5, 2005 9:54 AM, E. Weddington <address@hidden> wrote:
> intiha Ho gai wrote:
> 
> >Thank you.
> >Okay.. i can live with that.. for now.. but my issue is.. will the
> >long long addition be correct?
> >Also if it is, then why isnt the solution for the equation to
> >calculate a (slope) and b(offset) coming out incorrect. For the above
> >code where I hand coded the values of all long longs
> >   table.sumX = 12338578LL;
> >       table.sumY = -3336078LL;
> >       table.sumXSquared = 7260107358192LL;
> >       table.sumXY = -1646741910392LL;
> >        denom = ( table.n * table.sumXSquared - table.sumX * table.sumX);
> >        if (denom != 0)
> >               a = (double)( table.n * table.sumXY - table.sumY *
> >table.sumX) / denom;
> >        b = (double)(table.sumY - a * table.sumX) / table.n;
> >
> >     sprintf(OutputMsg,"**************** A=%f     B=%f ***********\r\n",a,b);
> >     UARTOutput(DBG_ERROR,"%s", &OutputMsg);
> >
> >I get on the UART
> >
> >**************** A=-0.045255     B=-106838.632813 ***********
> >
> >While the actual values of a and b that i have precomputed should be a
> >= -0.000208 , and b = -133340.419011
> >
> >
> What is the value of table.n that you are using in the code above to get
> the results that you gave?
> 
> Is table.sumXSquared supposed to be the square of table.sumX?
> 
> Please give us more information about what you are doing here.
> 
> Also, could you post/attach the assembly output of the above code snippet?
> 
> Eric
> 
table.n =25 and no table.sumXSquared is not the square of table.sumX,
it is the sum of the sqaure of each datapoint x. it is Summation(x^2)
not (Summantion(x))^2. I have done the same calculation on a similar
code that works on my desktop to generate the above values for a, and
b.
I will post the assembly portion soon.. (If i am right i just use the
-S option while compiling right?- I am new to this :) ).

Thanks.
Affan




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