Special case: matrix size 1

src/elpa1/elpa1_template.F90

@@ -122,6 +122,7 @@ function elpa_solve_evp_&
    &PRECISION&
    &")
 
+   success = .true.
 
    if (present(q)) then
      obj%eigenvalues_only = .false.
@@ -136,6 +137,28 @@ function elpa_solve_evp_&
    nblk       = obj%nblk
    matrixCols = obj%local_ncols
 
+   ! special case na = 1
+   if (na .eq. 1) then
+#if REALCASE == 1
+     ev(1) = a(1,1)
+     if (.not.(obj%eigenvalues_only)) then
+       q(1,1) = CONST_REAL_1_0
+     endif
+#endif
+#if COMPLEXCASE == 1
+     ev(1) = real(a(1,1))
+     if (.not.(obj%eigenvalues_only)) then
+       q(1,1) = CONST_COMPLEX_PAIR_1_0
+     endif
+#endif
+     call obj%timer%stop("elpa_solve_evp_&
+     &MATH_DATATYPE&
+     &_1stage_&
+     &PRECISION&
+     &")
+     return
+   endif
+
    if (nev == 0) then
      nev = 1
      obj%eigenvalues_only = .true.
@@ -167,7 +190,6 @@ function elpa_solve_evp_&
 #endif
 
    call obj%timer%stop("mpi_communication")
-   success = .true.
 
    call obj%get("debug", debug)
    wantDebug = debug == 1

src/elpa2/elpa2_template.F90

@@ -123,6 +123,8 @@
     &PRECISION&
     &")
 
+    success = .true.
+
     if (present(q)) then
       obj%eigenvalues_only = .false.
     else
@@ -136,6 +138,28 @@
     nblk       = obj%nblk
     matrixCols = obj%local_ncols
 
+   ! special case na = 1
+   if (na .eq. 1) then
+#if REALCASE == 1
+     ev(1) = a(1,1)
+     if (.not.(obj%eigenvalues_only)) then
+       q(1,1) = CONST_REAL_1_0
+     endif
+#endif
+#if COMPLEXCASE == 1
+     ev(1) = real(a(1,1))
+     if (.not.(obj%eigenvalues_only)) then
+       q(1,1) = CONST_COMPLEX_PAIR_1_0
+     endif
+#endif
+     call obj%timer%stop("elpa_solve_evp_&
+     &MATH_DATATYPE&
+     &_2stage_&
+     &PRECISION&
+     &")
+     return
+   endif
+
    if (nev == 0) then
      nev = 1
      obj%eigenvalues_only = .true.
@@ -210,7 +234,6 @@
 
     call obj%get("debug",debug)
     wantDebug = debug == 1
-    success = .true.
 
     do_useGPU      = .false.
     do_useGPU_trans_ev_tridi =.false.

src/elpa2/legacy_interface/elpa2_template.F90

@@ -204,61 +204,63 @@
       return
     endif
 
-    time_evp_fwd = e%get_time("elpa_solve_evp_&
-   &MATH_DATATYPE&
-   &_2stage_&
-   &PRECISION&
-   &","bandred")
-
-   if (my_prow==0 .and. my_pcol==0 .and. elpa_print_times) &
-      write(error_unit,*) 'Time bandred_real               :', time_evp_fwd
-
-   time_evp_fwd =  time_evp_fwd + e%get_time("elpa_solve_evp_&
-   &MATH_DATATYPE&
-   &_2stage_&
-   &PRECISION&
-   &","tridiag")
-
-   if (my_prow==0 .and. my_pcol==0 .and. elpa_print_times) &
-      write(error_unit,*) 'Time tridiag_band_real          :',e%get_time("elpa_solve_evp_&
-   &MATH_DATATYPE&
-   &_2stage_&
-   &PRECISION&
-   &","tridiag")
-
-   time_evp_solve = e%get_time("elpa_solve_evp_&
-   &MATH_DATATYPE&
-   &_2stage_&
-   &PRECISION&
-   &","solve")
-
-   if (my_prow==0 .and. my_pcol==0 .and. elpa_print_times) &
-     write(error_unit,*) 'Time solve_tridi                :',time_evp_solve
-
-   time_evp_back = e%get_time("elpa_solve_evp_&
-   &MATH_DATATYPE&
-   &_2stage_&
-   &PRECISION&
-   &","trans_ev_to_band")
-
-   if (my_prow==0 .and. my_pcol==0 .and. elpa_print_times) &
-     write(error_unit,*) 'Time trans_ev_tridi_to_band_real:',time_evp_back
-
-   time_evp_back = time_evp_back  + &
-   e%get_time("elpa_solve_evp_&
-   &MATH_DATATYPE&
-   &_2stage_&
-   &PRECISION&
-   &","trans_ev_to_full")
-
-   if (my_prow==0 .and. my_pcol==0 .and. elpa_print_times) &
-     write(error_unit,*) 'Time trans_ev_band_to_full_real :',e%get_time("elpa_solve_evp_&
-   &MATH_DATATYPE&
-   &_2stage_&
-   &PRECISION&
-   &","trans_ev_to_full")
-
-
+    if (na .gt. 1) then
+      time_evp_fwd = e%get_time("elpa_solve_evp_&
+      &MATH_DATATYPE&
+      &_2stage_&
+      &PRECISION&
+      &","bandred")
+
+      if (my_prow==0 .and. my_pcol==0 .and. elpa_print_times) &
+        write(error_unit,*) 'Time bandred_real               :', time_evp_fwd
+
+      time_evp_fwd =  time_evp_fwd + e%get_time("elpa_solve_evp_&
+      &MATH_DATATYPE&
+      &_2stage_&
+      &PRECISION&
+      &","tridiag")
+
+      if (my_prow==0 .and. my_pcol==0 .and. elpa_print_times) &
+        write(error_unit,*) 'Time tridiag_band_real          :',e%get_time("elpa_solve_evp_&
+        &MATH_DATATYPE&
+        &_2stage_&
+        &PRECISION&
+        &","tridiag")
+
+      time_evp_solve = e%get_time("elpa_solve_evp_&
+      &MATH_DATATYPE&
+      &_2stage_&
+      &PRECISION&
+      &","solve")
+
+      if (my_prow==0 .and. my_pcol==0 .and. elpa_print_times) &
+        write(error_unit,*) 'Time solve_tridi                :',time_evp_solve
+
+      if (nev .ge. 1) then
+        time_evp_back = e%get_time("elpa_solve_evp_&
+        &MATH_DATATYPE&
+        &_2stage_&
+        &PRECISION&
+        &","trans_ev_to_band")
+
+      if (my_prow==0 .and. my_pcol==0 .and. elpa_print_times) &
+        write(error_unit,*) 'Time trans_ev_tridi_to_band_real:',time_evp_back
+
+      time_evp_back = time_evp_back  + &
+      e%get_time("elpa_solve_evp_&
+      &MATH_DATATYPE&
+      &_2stage_&
+      &PRECISION&
+      &","trans_ev_to_full")
+
+      if (my_prow==0 .and. my_pcol==0 .and. elpa_print_times) &
+        write(error_unit,*) 'Time trans_ev_band_to_full_real :',e%get_time("elpa_solve_evp_&
+       &MATH_DATATYPE&
+       &_2stage_&
+       &PRECISION&
+       &","trans_ev_to_full")
+      endif
+    endif ! na > 1
     call elpa_deallocate(e)
 
     call elpa_uninit()

test/shared/test_analytic.F90

@@ -238,7 +238,11 @@ module test_analytic
     ! go to zero-based indexing
     ii = i - 1
     jj = j - 1
-    a = exp(log(largest_ev)/(na-1))
+    if (na .gt. 2) then
+      a = exp(log(largest_ev)/(na-1))
+    else
+      a = exp(log(largest_ev)/(1))
+    endif
     s = 0.5_rk8
     c = sqrt(3.0_rk8)/2.0_rk8
     element = ONE