Fix: spmv y-reset bug and add error guard in tridiagonal init

Author: Mahmood-Sinan

src/stdlib_specialmatrices_tridiagonal.fypp

@@ -103,10 +103,12 @@ submodule (stdlib_specialmatrices) tridiagonal_matrices
             call linalg_error_handling(err0, err)
         endif
 
-        ! Description of the matrix.
-        A%n = n
-        ! Matrix elements.
-        A%dl = dl ; A%dv = dv ; A%du = du
+        if(err0%ok()) then
+            ! Description of the matrix.
+            A%n = n
+            ! Matrix elements.
+            A%dl = dl ; A%dv = dv ; A%du = du
+        endif
     end function
 
     module function initialize_constant_tridiagonal_impure_${s1}$(dl, dv, du, n, err) result(A)
@@ -124,16 +126,19 @@ submodule (stdlib_specialmatrices) tridiagonal_matrices
         integer(ilp) :: i
         type(linalg_state_type) :: err0
 
-        ! Description of the matrix.
-        A%n = n
         if (n <= 0) then
             err0 = linalg_state_type(this, LINALG_VALUE_ERROR, "Matrix size needs to be positive, n = ", n, ".")
             call linalg_error_handling(err0, err)
         endif
-        ! Matrix elements.
-        A%dl = [(dl, i = 1, n-1)]
-        A%dv = [(dv, i = 1, n)]
-        A%du = [(du, i = 1, n-1)]
+        
+        if(err0%ok()) then
+            ! Description of the matrix.
+            A%n = n
+            ! Matrix elements.
+            A%dl = [(dl, i = 1, n-1)]
+            A%dv = [(dv, i = 1, n)]
+            A%du = [(du, i = 1, n-1)]
+        endif
     end function
     #:endfor
 
@@ -168,7 +173,7 @@ submodule (stdlib_specialmatrices) tridiagonal_matrices
         op_    = "N"        ; if (present(op))    op_    = op
 
         ! Prepare Lapack arguments.
-        n = A%n ; ldx = n ; ldy = n ; y = 0.0_${k1}$
+        n = A%n ; ldx = n ; ldy = n ;
         nrhs = #{if rank==1}# 1 #{else}# size(x, dim=2, kind=ilp) #{endif}#
 
         #:if rank == 1