Interpolation with pwrfit and solve equation with units

Question

Hello,I'm using a worksheet in Mathcad prime 11 with the pwrfit function to interpolate the curve of electronic components.Since I like working with units in Mathcad, I slightly modified the interpolation coefficients to include units.Solve this kind of equation, but with the interpolation VPROT = F(I). I is the resultMy goal is to solve a function that uses this interpolation. The solve function doesn't work, but I can find the solution for a single point using a solve block and the Find function.   Could you help me to solve the solve function 🙂 Thank youSee attached file.

ESAB · Accepted Answer

Hi Werner_E,

Thank you very much for your replying.

Initially, I wanted to solve it using an equation like: in order to determine I as a function of the parameters. But your solution ends up giving the same result, which is perfect.

Thank you and have a great day!"

Werner_E · Answer

The symbolics does not know anything about units. It does not know how amperes and ohms are related, or kilovolts and volts and treats them all as unknown variables. So using the symbolic "solve" usually makes more sense to apply to a symbolic equation without any variables being defined.

But as you are using an interpolating function found by "pwrfit" I guess you are not looking for a symbolic solution.

From what I see in your sheet you are just looking for a (numeric, but unit-aware) function dependent on R_S, correct?

You can get this by parametrizing the solve block, that way turning it into a function of R_S.

Instead of a solve block with "find" you could also use the "root" function:

Prime 11 file attached

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