We show that if a map
ϕ on the set of positive definite matrices satisfies
class="formula" id="fm0010">
then
ϕ is of the form
class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0024379516302403&_mathId=si2.gif&_user=111111111&_pii=S0024379516302403&_rdoc=1&_issn=00243795&md5=f64accf5a230b237bed81a00c0c3b70f" title="Click to view the MathML source">ϕ(A)=M⁎AMclass="mathContainer hidden">class="mathCode"> or
class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0024379516302403&_mathId=si24.gif&_user=111111111&_pii=S0024379516302403&_rdoc=1&_issn=00243795&md5=1333dab2b0ec564ee7e0feba4c640a98" title="Click to view the MathML source">ϕ(A)=M⁎AtMclass="mathContainer hidden">class="mathCode"> for some invertible matrix
M with
class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0024379516302403&_mathId=si158.gif&_user=111111111&_pii=S0024379516302403&_rdoc=1&_issn=00243795&md5=71149d4f10bbad555d7da644bca9e943" title="Click to view the MathML source">det(M⁎M)=1class="mathContainer hidden">class="mathCode">. We also characterize the map
class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0024379516302403&_mathId=si5.gif&_user=111111111&_pii=S0024379516302403&_rdoc=1&_issn=00243795&md5=8538e2357e694faa882abc949be46387" title="Click to view the MathML source">ϕ:S→Sclass="mathContainer hidden">class="mathCode"> preserving the similar trace equality or the determinant equality
class="formula" id="fm0020">
in class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0024379516302403&_mathId=si7.gif&_user=111111111&_pii=S0024379516302403&_rdoc=1&_issn=00243795&md5=bc9c9ccfeee18592478b3d847a13dc9c" title="Click to view the MathML source">Sclass="mathContainer hidden">class="mathCode">, where class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0024379516302403&_mathId=si7.gif&_user=111111111&_pii=S0024379516302403&_rdoc=1&_issn=00243795&md5=bc9c9ccfeee18592478b3d847a13dc9c" title="Click to view the MathML source">Sclass="mathContainer hidden">class="mathCode"> denotes the set of complex matrices, symmetric matrices, or upper triangular matrices, respectively.