P A C K A G E DTENSBS (Version 1982 ) Subprograms for interpolation of two and three dimensional gridded data using tensor products of B-spline basis functions. This is a double precision version of the package TENSBS. By two dimensional gridded data we mean data of the form (x(i), y(j), f(x(i),y(j))) i=1,..,nx, j=1,..,ny. The subprograms in this package determine a piecewise polynomial function S(x,y) such that S(x(i),y(j)) = f(x(i),y(j)) i=1,..,nx, j=1,..,ny. The function S takes the form nx ny S(x,y) = SUM SUM a U (x) V (y) i=1 j=1 ij i j where U(i) and V(j) are fixed one-dimensional piecewise polynomial functions (the B-spline basis functions of the reference). The user specifies the order (degree+1) of the polynomial pieces that define the function S in each direction. The resulting interpolant will have continuous derivatives of up to order-2 in each direction. For example, if the user specifies order 4 in x and order 3 in y, then the functions U(i) will be piecewise cubic polynomials while the functions V(j) will be piecewise quadratics. The resulting interpolating function will have continuous first and second partial derivatives with respect to x and continuous first partial derivative with respect to y. (Lower continuity can be obtained by using the option for user-specified "knots" -- see the reference.) The subroutines in this package are DB2INK........computes parameters that define a piecewise polynomial function that interpolates a given set of two-dimensional gridded data. DB2VAL........evaluates the interpolating function determined by DB2INK or one of its derivatives. DB3INK........computes parameters that define a piecewise polynomial function that interpolates a given set of three-dimensional gridded data. DB3VAL........evaluates the interpolating function determined by DB3INK or one of its derivatives. Reference Carl de Boor, A Practical Guide to Splines, Springer-Verlag, New York, 1978.