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Jan 19, 2009 12:10 PM
(589 views)

Parameter({theta1 = 1, theta2 = 1, b2 = 20, b3 = 1, b4 = 1},

If( :Pore Size - b2 < 0, 1 / (1 + theta1 * Exp(theta2 * ( :Pore Size - 10))),

1 / (1 + b3 * Exp(b4 * ( :Pore Size - 10)))))

But when I run nonlinear with this model, JMP will not vary b2--it keeps it fixed.

Any help out there?

2 REPLIES

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Jan 21, 2009 5:25 AM
(544 views)

If( criterion,

model1,

model2

);

I am not sure about b2 as a parameter. Is this criterion set independently or is it fit from the data? You might want to replace b2 with constant if it is the former use.

Another way is to use a Boolean expression as a multiplier in one model that includes both forms. In this way, the logic determines which form contributes to the model for a particular value of X:

(criterion)*model1 + Not(criterion)*model2;

Learn it once, use it forever!

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Jan 22, 2009 5:30 AM
(544 views)

Anyway, I did stumble upon using the boolean multiplier approach. I was trying to set b2 from the data as an unknown point. I was trying to knit to functions together to fit the data better. I've found that nonlinear can be very sensitive--if I ask something that causes difficulty it can really be a pain as I'm attempting to fit 140+ curves at once.