06-20-2015, 04:01 PM

Can anyone tell me what I am doing wrong?

I plotted the function ph2o(X) (code below) and touched Menu/Fcn/Tangent and, as expected, I saw the tangent line at the cursor location that I could trace up and down the curve.

[attachment=2185]

However, when I plot function tdew(X,15) (code also below) and touch the tangent soft-key I get nothing. When I touch slope I get NaN.

[attachment=2187]

I get the same result with newton, newtonj, and bisection solver. Am I doing something wrong, or is the calculator not capable of that operation on that function?

Thanks for reading,

Paul

I plotted the function ph2o(X) (code below) and touched Menu/Fcn/Tangent and, as expected, I saw the tangent line at the cursor location that I could trace up and down the curve.

[attachment=2185]

However, when I plot function tdew(X,15) (code also below) and touch the tangent soft-key I get nothing. When I touch slope I get NaN.

[attachment=2187]

I get the same result with newton, newtonj, and bisection solver. Am I doing something wrong, or is the calculator not capable of that operation on that function?

Thanks for reading,

Paul

Code:

EXPORT ph2o(temp)

BEGIN

local a,b;

b:=(temp+273.15)/273.16;

a:=1-1/b;

return 10^(10.79574*a-5.028*log(b,10)+

1.50475ᴇ−4*(1-10^(−8.2969*(b-1)))+

4.2873ᴇ−4*(10^(4.76955*a)-1)-0.2138602);

END;

export tdew(r,tamb)

begin

LOCAL y,z;

r:=ph2o(tamb)*r/100;

z:="fsolve(ph2o(x)="+STRING(r,2,12)+",x,−50 .. 100, newton_solver)";

y:=CAS(z);

RETURN y(1);

END;