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Hi Ted,
In a mod file of sodium channel Hodgkin-Huxley style kinetics, tha is a parameter that used to determine the 1/2 voltage of activation. Tha is always a constant during the stimulation. However, I want to make it change with time. For instance, tha will become more and more negtive with the time going. What should I do? I have tried to declare tha in ASSIGNED block and write the arithmetic expression (such as tha=-28+10*exp(-1*t/0.01)) in the same PROCEDURE which is also used to calculate minf & mtau, but it doesn't work.

qianhao wrote:tha=-28+10*exp(-1*t/0.01))

tha = -18 at t==0 and collapses toward -28 with a time constant of 0.01 ms. By t==0.05 ms, tha is practically identical to -28. Is that what you want?

Thank you! Ted.
I have resolve this problem. The wrong point in my code is that
It means that t will be a constant during the calculation of m & h, isn't it?

The TABLE statement is worse than useless if you intend to change tha in the course of a simulation.
Comment it out (insert a colon ":" in front of the word TABLE).