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cjaya.2
cjaya.2
Associate III
February 2, 2024
Question

work out poly

  • February 2, 2024
  • 1 reply
  • 1299 views

Need a help to work out the formula. I cant get my head around with this to work out. its polynomial with numerator and denominator. what is the formula for this. Thank you

 

FLOAT_TYPE num_coeff[] = {-2.42580348918581e2l, 4.43575581447635e2l, -8.6570608699616e2l, 7.34933695653457e2l, -7.02396810482965e1l};

FLOAT_TYPE den_coeff[] = {1.e0l, -8.87493143817912e-1l, 2.75291524634514e0l, -3.88521936154463e-1l, 9.08722079164108e-3l};

FLOAT_TYPE num_poly = num_coeff[sizeof(num_coeff) / sizeof(num_coeff[0]) - 1];

FLOAT_TYPE den_poly = den_coeff[sizeof(den_coeff) / sizeof(den_coeff[0]) - 1];

for (int i = (sizeof(num_coeff) / sizeof(num_coeff[0]) - 2); i >= 0; --i)

   {

   num_poly = num_poly * r + num_coeff[i];

} 

for (int i = (sizeof(den_coeff) / sizeof(den_coeff[0]) - 2); i >= 0; --i)

  {

  den_poly = den_poly * r + den_coeff[i]; } return (num_poly / den_poly);

  }

1 reply

TDK
TDK
Super User
February 2, 2024

num_poly(x) and den_poly(x) are each polynomials.

Result gives you num_poly(x) / den_poly(x).

Here, num_poly(x) = -2.42580348918581e2 + 4.43575581447635e2 * x - 8.6570608699616e2l * x^2 + 7.34933695653457e2 * x^3 - 7.02396810482965e1 * x^4

And den_poly(x) = 1.e0 - 8.87493143817912e-1 * x + 2.75291524634514e0 * x^2 - 3.88521936154463e-1 * x^3 + 9.08722079164108e-3l * x^4

 

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cjaya.2
cjaya.2Author
Associate III
February 4, 2024

Thank you for the reply and formula. When I did the excel calculation on this I get a different answer using the above formula. But When I complie it I get different answer. Why is that

These are the numbers for derived formula.

1.000
1.038
1.057
1.067
1.077
1.081
1.085
1.089
1.092
1.096
1.100
1.104
1.108
1.112
1.116
1.193
1.289
1.385
cjaya.2
cjaya.2Author
Associate III
February 4, 2024

float res2temp(float r)

{

  int ni;

FLOAT_TYPE num_poly = num_coeff[sizeof(num_coeff) / sizeof(num_coeff[0]) - 1]; FLOAT_TYPE den_poly = den_coeff[sizeof(den_coeff) / sizeof(den_coeff[0]) - 1];

for (ni = (sizeof(num_coeff) / sizeof(num_coeff[0]) - 2); ni >= 0; --ni)

{

num_poly = num_poly * r + num_coeff[ni];

}

for (int i = (sizeof(den_coeff) / sizeof(den_coeff[0]) - 2); i >= 0; --i)

{

den_poly = den_poly * r + den_coeff[i];

}

return (num_poly / den_poly);

}

 

In this function I pass res2temp(6.e4f * adc_result / (1074547130368ll - (3ll * adc_result)))

The adc_result I putting are,

17909418.84,
18598931.46,
18944583.25,
19116513.67,
19288444.09,

19358290.82,

19426346.62,

19496193.35
,19564249.14
,19634095.87
,19702151.67
,19771998.4
,19840054.19
,19909900.92
,19977956.72
,21356981.97
,23081659
,24804545.09

its the same numbers when calculated adc_result, I mentioned above entering into excel but why excel gives different answer?

 

 

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