fix bug for Id

Author: TendonFFF

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased](https://github.com/qutip/QuantumToolbox.jl/tree/main)
 
+- Add functions for `brmesolve`
+
 ## [v0.31.1]
 Release date: 2025-05-16
 

src/time_evolution/brmesolve.jl

@@ -110,6 +110,7 @@ function _brterm(
     _check_br_spectra(spectra)
 
     U, N = rst.vectors, prod(rst.dimensions)
+    Id = I(N)
 
     skew = @. rst.values - rst.values' |> real
     spectrum = spectra.(skew)
@@ -125,7 +126,6 @@ function _brterm(
         ac_term .*= m_cut
         bd_term .*= m_cut
 
-        Id = I(N)
         vec_skew = vec(skew)
         M_cut = @. abs(vec_skew - vec_skew') < sec_cutoff
     end