function [Ju, Jv, checkval] = get_approximate_jacobian(trimfile,n,m,t)
nefisopt = 'quiet';
NFS = vs_use(trimfile,nefisopt);
lsedbl = vs_get(NFS,'map-const','LSEDBL','quiet'); % not equal to lsedtot, but will do for now
Nj = lsedbl + 3;

checkval = vs_get(NFS,'map-sed-series',{t},'HIRCHK',{n,m},nefisopt);
Ju = vs_get(NFS,'map-sed-series',{t},'HIRJCU',{n,m,1:Nj^2},nefisopt);
Ju = reshape(Ju(:),Nj,Nj);

Jv = vs_get(NFS,'map-sed-series',{t},'HIRJCV',{n,m,1:Nj^2},nefisopt);
Jv = reshape(Jv(:),Nj,Nj);
end