Constant STI_DEFAULT_NITER 

pub const STI_DEFAULT_NITER: usize = 100;

QSM_iLSQR’s own iteration cap, used when it is called without 'niter' (output bitwise equal to an explicit 100), as UK Biobank’s pipeline and STI Suite’s STI_Templates.m call it, and the default of IlsqrParams::max_iter.