On The Shape Preserving Approximation

Sometimes one may desire to approximate a function defined on a finite interval (for example [-1,1]), subject to the conservation of so called shape properties (positivity, monotonicity and convexity). The first contribution is that we have approximated a function from a space Lp[-1,1], 0 > p, by a number of piecewise linear functions and we have obtained global estimate of each of them using the second order of Ditzian ¿ Totik modulus of smoothness. Furthermore, these piecewise linear functions preserves the positivity of the function. Also proved the rate of coconvex approximation in the Lp[-1,1] spaces, in terms of the third order of Ditzian ¿ Totik modulus of smoothness, where the constants involved depend on the location of the points of change of convexity. We have thus filled up a gap due to the uncertainty between previously known estimates involving the second order of Ditzian ¿ Totik modulus of smoothness and the impossibility of having such estimates involving with the second order of usual modulus of smoothness.