ngspice ltvspice netlist compatibility problems
The LIMIT() is not defined in NGspice.
According to the NGspice manual:


  16.13.2 Missing functions
  You may add one or more function definitions to your input file, as listed below.  


     .func LIMIT(x,a,b) {min(max(x, a), b)}
     .func PWR(x,a) {abs(x) ** a}
     .func PWRS(x,a) {sgn(x) * PWR(x,a)}
     .func stp(x) {u(x)}