シンプソンの公式 I

Simpson's Rule estimates areas when exact mathematical equations are unavailable, such as land between a straight road and a curved riverbank. By fitting a parabola through three equally spaced sample points and integrating the resulting quadratic function, surveyors can accurately approximate irregular land areas using only perpendicular distance measurements without needing a precise riverbank equation.

Simpson's Rule fits a unique parabola through three equally spaced points on a curve. The midpoint measurement allows the constant term of the quadratic function to be determined directly. Substituting this value into expressions for the remaining points reduces the equation to one involving only the measured distances, commonly denoted as y0, y1, and y2.

Surveyors measure perpendicular distances from a straight road to a curved riverbank at three equally spaced positions along the land strip. These three measured distances serve as the data points used to construct the approximating parabola, providing the sampled values needed to estimate the total area of the irregular land.

Simpson's Rule is a numerical integration method that approximates the value of a definite integral when an exact antiderivative is difficult or impossible to obtain. By integrating the quadratic function fitted through three points and applying limits, Simpson's Rule yields a formula for estimated area in terms of spacing and sampled values, making approximate integration practical for real-world applications.

The center point measurement allows the constant term C of the quadratic function to be determined immediately. Substituting this constant into the outer point expressions and solving reduces the formula to an expression involving only y0, y1, and y2, streamlining the calculation of estimated area for irregular land strips.

Simpson's Rule provides accurate approximations for many smoothly varying functions by using only a small number of sampled values. The method's accuracy stems from fitting a parabola through three equally spaced points, which effectively captures the curvature of smooth boundaries like riverbanks, making it reliable for practical surveying applications.

After mathematically fitting a parabola through three points, the area under the parabola is found by integrating the quadratic equation over the interval. Solving the integral, applying limits, and substituting the measured distances y0, y1, and y2 yields the final formula for estimated area expressed in terms of spacing h and the sampled values.