Merge pull request #674 from suny-downstate-medical-center/netpyne_joao

added a missing ghk.inc mod file in the batchCell example

examples/batchCell/mod/ghk.inc

@@ -0,0 +1,40 @@
+COMMENT
+    GHK function that returns effective driving force
+    Slope at low voltages is 1
+    z needs to be set as a PARAMETER
+ENDCOMMENT
+
+FUNCTION ghkg(v(mV), ci(mM), co(mM), z) (mV) {
+    LOCAL xi, f, exi, fxi
+    f = R*(celsius+273.15)/(z*(1e-3)*FARADAY)
+    xi = v/f
+    exi = exp(xi)
+    if (fabs(xi) < 1e-4) {
+        fxi = 1 - xi/2
+    }else{
+        fxi = xi/(exi - 1)
+    }
+    ghkg = f*((ci/co)*exi - 1)*fxi
+}
+
+FUNCTION ghk(v(mV), ci(mM), co(mM), z) (.001 coul/cm3) {
+    LOCAL xi, f, exi, fxi
+    f = R*(celsius+273.15)/(z*(1e-3)*FARADAY)
+    xi = v/f
+    exi = exp(xi)
+    if (fabs(xi) < 1e-4) {
+        fxi = 1 - xi/2
+    }else{
+        fxi = xi/(exi - 1)
+    }
+    ghk = (.001)*z*FARADAY*(ci*exi - co)*fxi
+}
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