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Defining a Piecewise function of two variables
Posted Dec 3, 2012, 1:03 p.m. EST 2 Replies
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Hello,
I am trying to model NMR diffusion in COMSOL 4.3 and need to define a function beta at three different time intervals as follows:
beta = gyro*(g*x) (0 < t < 0.016s)
beta = 0 (0.016s < t < 0.040s)
beta = gyro*(-g*x) (0.040s < t < 0.056s)
x is the displacement in (m) and gyro and g are constants
I have defined three analytic functions for beta as functions of x. I am not sure how to use this to define a piecewise function for the three different time intervals. I am new to COMSOL and would be really grateful for any help with this.
Thank you,
Caroline
I am trying to model NMR diffusion in COMSOL 4.3 and need to define a function beta at three different time intervals as follows:
beta = gyro*(g*x) (0 < t < 0.016s)
beta = 0 (0.016s < t < 0.040s)
beta = gyro*(-g*x) (0.040s < t < 0.056s)
x is the displacement in (m) and gyro and g are constants
I have defined three analytic functions for beta as functions of x. I am not sure how to use this to define a piecewise function for the three different time intervals. I am new to COMSOL and would be really grateful for any help with this.
Thank you,
Caroline
2 Replies Last Post Dec 3, 2012, 4:17 p.m. EST
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Posted:
1 decade ago
Hi
what abut combining 2 step functions in an analytical function, with a step from +1 to 0 at offset t=0.016, and one from 0 to -1 at t=0.04, and then the analytical funxtion ana1 = gyro*(g*x)*(stp1(t)+stp2(t))
or something like that, its nce with the analytical functions, as you might define units and plot the result to check it out carefully, before solving blindly ;)
--
Good luck
Ivar
what abut combining 2 step functions in an analytical function, with a step from +1 to 0 at offset t=0.016, and one from 0 to -1 at t=0.04, and then the analytical funxtion ana1 = gyro*(g*x)*(stp1(t)+stp2(t))
or something like that, its nce with the analytical functions, as you might define units and plot the result to check it out carefully, before solving blindly ;)
--
Good luck
Ivar
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Posted:
1 decade ago
Thanks, that worked ! :)