  A new closed formula for the first order perturbation estimate of the mixed
least squares-total least squares (MTLS) solution is presented. It is
mathematically equivalent to the one by Zheng and Yang(Numer. Linear Algebra
Appl. 2019; 26(4):e2239). With this formula, general and structured normwise,
mixed and componentwise condition numbers of the MTLS problem are derived.
Perturbation bounds based on the normwise condition number, and compact forms
for the upper bounds of mixed and componentwise condition numbers are also
given in order for economic storage and efficient computation. It is shown that
the condition numbers and perturbation bound of the TLS problem are unified in
the ones of the MTLS problem.
