Neotech,
In what area does get ground height and gravity compare to eachother? If using a matrix in your level, you must implement both to have the effect of falling and of a solid ground beneath the player.
To make a character jump , you need two variables. One for height and the other for negative/positive acceleration. When the user taps the "jump" key, maybe the spacebar for instance, then the acceleration variable should be set to some larger positive value. By adding the acceleration variable to the characters current postition, the character will move at an upwards motion, at the rate you set.
When the character is in "jump mode", within the air after pressing the jump key, so to say, the acceleration of the jump needs to decrease by gravity, eventually forming into a negative value.
+NanoBrain+
