Conform to _compute_jacobian in factor block difference

include/core/factor/factor_block_difference.h

@@ -153,11 +153,11 @@ inline void FactorBlockDifference::evaluateJacobians(const std::vector<Eigen::Ma
     assert(getMeasurementSquareRootInformationUpper().cols() == J_res_sb1_.rows() && "Wrong jacobian sb1 or covariance size");
     assert(getMeasurementSquareRootInformationUpper().cols() == J_res_sb2_.rows() && "Wrong jacobian sb2 or covariance size");
 
-    // normalized jacobian
-    if (_jacobians[0].size() > 0){
+    // normalized jacobian, computed according to the _compute_jacobian flag
+    if (_compute_jacobian[0]){
         _jacobians[0] = getMeasurementSquareRootInformationUpper() * J_res_sb1_;
     }
-    if (_jacobians[1].size() > 0){
+    if (_compute_jacobian[1]){
         _jacobians[1] = getMeasurementSquareRootInformationUpper() * J_res_sb2_;
     }
 }
@@ -176,11 +176,11 @@ inline void FactorBlockDifference::evaluateJacobians(const std::vector<Eigen::Ma
     assert(getMeasurementSquareRootInformationUpper().cols() == J_res_sb1_.rows() && "Wrong jacobian sb1 or covariance size");
     assert(getMeasurementSquareRootInformationUpper().cols() == J_res_sb2_.rows() && "Wrong jacobian sb2 or covariance size");
 
-    // normalized jacobian
-    if (_jacobians[0].size() > 0){
+    // normalized jacobian, computed according to the _compute_jacobian flag
+    if (_compute_jacobian[0]){
         _jacobians[0] = getMeasurementSquareRootInformationUpper() * J_res_sb1_;
     }
-    if (_jacobians[1].size() > 0){
+    if (_compute_jacobian[1]){
         _jacobians[1] = getMeasurementSquareRootInformationUpper() * J_res_sb2_;
     }
 }