Plots per-component standard deviations (or approximate singular values if running PCAFast),
percent variance explained per principal component, or cumulative percent variance explained,
to help pick an elbow in the graph. This elbow often corresponds well with significant
dimensions and is much faster to run than Jackstraw.
Number of dimensions to plot (positive integer; capped by stored components)
reduction
Reduction technique to plot (default is 'pca')
plot_type
One of "stdev" (default), "variance" (per-PC % variance), or
"cumulative_variance" (running sum of those percentages; equals 100% at the last
stored PC when ndims spans all of them)