# Pseudo-Time Is Not the Load Factor

In a nonlinear static analysis, the time series associated with lateral loads is typically linear:

ops.timeSeries('Linear',1)

In this case, the load factor, $\lambda$, associated with the time series is equal to the pseudo-time in the domain, i.e., $\lambda(t)=t$. Then, when you use the '-time' option in the node and element recorders, you get the load factor “for free”, i.e., without any additional effort.

However, the load factor is not always equal to the pseudo-time in a static analysis. For example, a little-used option lets you supply a factor to the linear time series:

ops.timeSeries('Linear',1,'-factor',0.8)

In this case, the load factor is $\lambda(t)=0.8t$. In other words, for every pseudo-time step of 1.0, the load factor will increase by 0.8 (or whatever factor you give).

There are other time series, e.g., Trig, Pulse, and Path, where the pseudo-time and load factor are not equal. But using a factor with the Linear time series was the most notable counter-example that came to mind.

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